SIGNAL MONITORING SYSTEM FIELD OF THE DISCLOSURE The present disclosure relates generally to a system for reliably detecting signal status especially in a railway environment. BACKGROUND OF THE DISCLOSURE Vehicles traversing various light and heavy railway networks around the world are typically driven by an on board human operator on predefined routes between stations. The operator driving the vehicle on the network is supported by numerous train control, communications and management computer systems which are often in communication with a control room(s). Standard protocols and procedures developed based upon operational considerations including vehicle type, vehicle speed, population density, time table etc. implemented in the various computer systems and by driver training help manage the inevitable risks associated with large vehicles travelling at speed with an extremely long stopping distance. Various safety critical signaling systems deployed adjacent railway tracks provide signals (e.g. signal lights) visible to human operators for control of the movement of vehicles throughout the network. In some parts of the rail network, especially in controllable closed environments on predictable predefined routes, trains may even be driven solely by computer without an on board human operator. In other parts of the rail network, (e.g. depots or other “Dark Territories”) railway vehicles are primarily under the manual control of the on-board human operator. In these locations, the railway vehicles may be driven on non-standard routes. In such dynamic environments, the movement of multiple vehicles on adjacent tracks means potential for human error is significant, especially if a visual signal is not observed by a human operator e.g. due to inadvertent distraction, fatigue etc. As would be appreciated, these errors may give rise to significant consequences. Current approaches to managing failure to observe signals in areas where railway vehicles are operating principally under manual control (especially in light rail) require expensive trackside modification to fit trackside balise or RFID tags which are then read by train mounted underframe readers. This position sensing system may be used with various systems for monitoring the state of signal infrastructure. MAIN\BOJOVI\39630035_1.docx 420626 Signaling infrastructure is a safety critical system, often run by a separate company such infrastructure is often inaccessible to an operator of a railway network. It would be appreciated that the components of the various systems which make up the signaling and railway infrastructure are generally safety critical systems the integrity of which must be maintained. One approach used to determine the operational state of the respective signal infrastructure (e.g. red light etc.) is by measuring signal current indirectly by monitoring current draw of the signal aspect panels. This information may be transmitted via gateways to a control room and then back to on board computers on trains creating latency and requiring significant modification. Any modifications (including structural, electrical, mechanical) to the operations of these systems are governed by rigorous and highly regulated standards, and so modifications would be expensive and may risk compromising the safety of the existing signaling system. Accordingly there is a need for providing a method and system for monitoring signals and corresponding movement of vehicles at a location which addresses or at least ameliorates some of the above issues. SUMMARY OF THE DISCLOSURE Features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or can be learned by practice of the herein disclosed principles. The features and advantages of the disclosure can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. In accordance with a first aspect of the present disclosure, there is provided a monitoring system for detecting the state of a signal installation including a vibration sensing unit engageable with a railway track at a location proximate to the signal installation and configured to detect a railway vehicle moving upon the railway track proximate to the vibration sensing unit and, upon detection of the railway vehicle, to broadcast sensor data including a unique sensor identifier; a state detecting unit engageable with the signal installation to receive visible light emitted therefrom and configured to broadcast detector data including a state indication of the signal installation and a unique detector identifier, wherein the unique detector identifier is associated with the unique sensor identifier; and an on-board computer disposed in the railway vehicle configured to receive the broadcast sensor data and the broadcast detector data, verify the association between the unique sensor identifier and the unique detector identifier and output the state of the signal installation if the association is verified. MAIN\BOJOVI\39630035_1.docx 420626 The monitoring system may include at least one additional vibration sensing unit spaced apart from the first vibration sensing unit; A unique sensor identifier of the additional vibration sensing unit may be associated with the unique sensor identifier of the first vibration sensing unit. The on-board computer may be configured to verify the association between the unique sensor identifier of the additional vibration sensing unit and the unique sensor identifier of the first vibration sensing unit. The on-board computer may be configured to verify that the sensor data from the first vibration sensing unit and sensor data from the additional vibration sensing unit are received in a predefined order. The unique sensor identifier may be identical to the unique detector identifier. The on-board computer may be configured to verify the association by checking that the unique sensor identifier and the unique detector identifier are identical. The vibration sensing unit may be configured to broadcast once upon detection of the railway vehicle and not broadcast again until a detected vibration level has passed below a predetermined threshold. The vibration sensing unit may be configured to enter a sleep state after a predetermined period of inactivity and awake from the sleep state in response to a detected vibration level which exceeds a predetermined threshold. The vibration sensing unit may be configured to transmit the sensor data using a high frequency chirp signal. The vibration sensing unit may be connected to one or more batteries disposed near to the vibration sensing unit. The state detecting unit may be configured to determine the state of the signal installation and broadcast the detector data based on the determined state. The state detecting unit may be configured to broadcast the detector data in response to determining that the state of the signal installation is a red light state. MAIN\BOJOVI\39630035_1.docx 420626 The state detecting unit may include an RGB light sensor configured to output RGB data and a processor configured to determine the state of the signal installation using an RGB/brightness/colour temperature algorithm based on the RGB data. The state detecting unit may be encapsulated in silicone and quartz crystal glass. The on-board computer may be configured to scan for the broadcast detector data in response to receiving the broadcast sensor data. The output of the on-board computer may include an identifier of the signal installation. In accordance with a second aspect of the present disclosure, there is provided a computer- implemented method of detecting the state of a signal installation, by detecting, using a vibration sensing unit engaged with a railway track at a location proximate to the signal installation, a railway vehicle moving upon the railway track proximate to the vibration sensing unit; broadcasting, by the vibration sensing unit upon detection of the railway vehicle, sensor data including a unique sensor identifier; receiving visible light emitted from the signal installation using a state detecting unit engaged with the signal installation; broadcasting, by the state detecting unit, detector data including a state indication of the signal installation and a unique detector identifier, wherein the unique detector identifier is associated with the unique sensor identifier; receiving the broadcast sensor data and the broadcast detector data using an on- board computer disposed in the railway vehicle; verifying, by the on-board computer, the association between the unique sensor identifier and the unique detector identifier; and outputting, by the on-board computer, the state of the signal installation if the association is verified. The method may include verifying, by the on-board computer, an association between the unique sensor identifier of the first vibration sensing unit and a unique sensor identifier of at least one additional vibration sensing unit spaced apart from the first vibration sensing unit. The method may include verifying, by the on-board computer, that the sensor data from the first vibration sensing unit and sensor data from the additional vibration sensing unit are received in a predefined order. Verifying the association may include checking that the unique sensor identifier and the unique detector identifier are identical. MAIN\BOJOVI\39630035_1.docx 420626 Broadcasting the sensor data may include broadcasting once upon detection of the railway vehicle and not broadcasting again until a detected vibration level has passed below a predetermined threshold. The method may include entering, by the vibration sensing unit, a sleep state after a predetermined period of inactivity. The method may include waking, by the vibration sensing unit, from the sleep state in response to a detected vibration level which exceeds a predetermined threshold. Broadcasting the sensor data may include transmitting the sensor data using a high frequency chirp signal. Broadcasting the detector data may include determining the state of the signal installation and broadcasting the detector data based on the determined state. Broadcasting the detector data may be in response to determining that the state of the signal installation is a red light state. Determining the state of the signal installation may include using an RGB/brightness/colour temperature algorithm based on RGB data output by an RGB light sensor. The method may include scanning, by the on-board computer, for the broadcast detector data in response to receiving the broadcast sensor data. Outputting the state of the signal installation may include outputting an identifier of the signal installation. In accordance with a third aspect of the present disclosure, there is provided a computer- readable medium comprising instructions which, when executed by a processor, cause the processor to detect, using a vibration sensing unit engaged with a railway track at a location proximate to the signal installation, a railway vehicle moving upon the railway track proximate to the vibration sensing unit; broadcast, by the vibration sensing unit upon detection of the railway vehicle, sensor data including a unique sensor identifier; receive visible light emitted from the signal installation using a state detecting unit engaged with the signal installation; broadcast, by the state detecting unit, detector data including a state indication of the signal installation and a unique detector identifier, wherein the unique detector identifier is associated with the unique sensor identifier; receive the broadcast sensor data and the broadcast detector data using an on-board computer disposed in the railway vehicle; verify, by the on-board computer, the MAIN\BOJOVI\39630035_1.docx 420626 association between the unique sensor identifier and the unique detector identifier; and output, by the on-board computer, the state of the signal installation if the association is verified. BRIEF DESCRIPTION OF THE DRAWINGS In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended Figures. Understanding that these Figures depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying Figures. Preferred embodiments of the present disclosure will be explained in further detail below by way of examples and with reference to the accompanying Figures, in which:- FIG 1A depicts a schematic diagram of an exemplary embodiment of the present disclosure when the monitoring system is deployed in a railway application. FIG 1B depicts a representative process flow of the system of the present disclosure and one exemplary implementation. FIG 2A depicts a schematic representation of an exemplary vibration sensing unit. FIG 2B depicts a perspective view of an exemplary vibration sensing unit mounted to a railway track. FIG 2C depicts a cross sectional view of a railway track to which an exemplary railway sensor has been mounted. FIG 3 depicts a schematic representation of an exemplary state detection unit. FIG 4 depicts a schematic representation of the main components of an exemplary on-board computer. FIG 5 depicts a flowchart of an exemplary method of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration MAIN\BOJOVI\39630035_1.docx 420626 purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the spirit and scope of the disclosure. The disclosed technology addresses the need in the art for a reliable and easily maintained system for monitoring the state of signals which does not interfere with existing infrastructure. Referring to Figure 1A, there is depicted an exemplary embodiment of a monitoring system 1 for detecting the state of a signal installation 2. The monitoring system 1 comprises a vibration sensing unit 10, a state detecting unit 20 and an on-board computer 30. The vibration sensing unit 10 is engageable with a railway track 3, as discussed in more detail below. The vibration sensing unit 10 is configured to detect a railway vehicle 4 moving upon the railway track 3 proximate to the vibration sensing unit 10. The vibration sensing unit 10 may be mounted in such a way that it is actuated by the presence of a railway vehicle 4 on the railway track 3. The railway vehicle 4 may be, for example, a train, locomotive, tram or any other vehicle configured for use on a conventional railway track or monorail track. Upon detection of the railway vehicle 4, the vibration sensing unit 10 is configured to broadcast sensor data 101 including a unique sensor identifier. In some examples, the unique sensor identifier may be unique to the vibration sensing unit 10 or it may be associated with an ID of the signal installation 2. For example, the vibration sensing unit 10 may be programmed onsite or remotely to have a unique sensor identifier which matches an ID of the signal installation 2. The vibration sensing unit 10 is mounted at a location proximate to the signal installation 2. In an exemplary embodiment the signal installation 2 is a traffic light which can change a plurality of states e.g. between a red light state, a green light state and optionally an amber light state. As is known in the art, the signal installation 2 may typically be controlled by a control box 5. The state detecting unit 20 is engageable with the signal installation 2 to receive visible light emitted therefrom. In this way, the state detecting unit 20 can determine the state of the signal installation 2 based on the emitted visible light. The state detecting unit 20 is configured to broadcast detector data 201 including a state indication of the signal installation 2 and a unique detector identifier. For example, the state detection unit may include a transmitter which may be mounted on or near the control box 5 for the corresponding signal installation 2. The unique detector identifier is associated with the unique sensor identifier. In some examples, the unique detector identifier may be unique to the MAIN\BOJOVI\39630035_1.docx 420626 state detecting unit 20 or it may be further associated with an ID of the signal installation 2. For example, the state detecting unit 20 may be programmed onsite or remotely to have a unique detector identifier which matches the ID of the signal installation 2. The on-board computer 30 is disposed in the railway vehicle 4. The on-board computer 30 is configured to receive the broadcast sensor data 101 and the broadcast detector data 201. For example, the on-board computer 30 may receive the broadcast signals through one or more communication interfaces. The on-board computer 30 is configured to verify the association between the unique sensor identifier and the unique detector identifier. For example, a processor 31 in the on-board computer 30 may be configured to match the unique sensor identifier against the unique detector identifier or, alternatively, the processor 31 may look up each of the unique sensor identifier and the unique detector identifier in a database 32 to verify if there is an association. If the association between the unique sensor identifier and the unique detector identifier is verified, the on-board computer 30 is configured to output the state of the signal installation 2. In this way, an accurate indication of the state of the signal installation 2 can be output. In particular, it can be ensured that the state corresponds to the signal installation 2 most proximate to the railway vehicle 4. By verifying an association between the unique sensor identifier and the unique detector identifier, the on-board computer 30 can ensure that the signals are received from a vibration sensing unit 10 and state detecting unit 20 installed near the same signal installation 2. In this way, the monitoring system 1 can ensure that the railway vehicle 4 is on the correct track corresponding to the signal installation 2 for which the state has been detected, before the state is output. This can prevent confusion between adjacent tracks and signal installations in close proximity, e.g. in a crowded depot. In some examples, the monitoring system 1 may include an additional vibration sensing unit 10B spaced apart from the first vibration sensing unit 10A. As shown, the vibration sensing units 10 may be spaced apart from each other by a distance “y”, e.g., by at least 1 metre or more. The first sensor data 101A broadcast by the first vibration sensing unit 10A and additional sensor data 101B broadcast by the additional vibration sensing unit 10B may each contain unique sensor identifiers. Detection of the railway vehicle 4 moving on the railway track 3 by the vibration sensing units 10 causes the sensor data 101A, 101B to be broadcast in succession, as the railway vehicle 4 moves in the direction marked with an arrow “A” and passes over the vibration sensing units 10. In this way, the monitoring system 1 can provide an indication of the direction of travel of the railway vehicle 4. MAIN\BOJOVI\39630035_1.docx 420626 In some examples, a unique sensor identifier of the additional vibration sensing unit 10B may be associated with the unique sensor identifier of the first vibration sensing unit 10A. The on-board computer 30 may be configured to verify the association between the unique sensor identifier of the additional vibration sensing unit 10B and the unique sensor identifier of the first vibration sensing unit 10A. In some examples, the on-board computer 30 may be configured to verify that the sensor data 101A from the first vibration sensing unit 10A and sensor data 101B from the additional vibration sensing unit 10B are received in a predefined order. In this way, the on- board computer 30 can additionally verify that the railway vehicle 4 is moving the in the correct direction along the track. If the sensor data 101A from the first vibration sensing unit 10A and sensor data 101B from the additional vibration sensing unit 10B are not received in a predefined order, the data may be discarded or ‘blacklisted’ as an improper reading. Alternatively, in some examples an alert may be output for manual checking by a user. In some examples, the monitoring system 1 may be include two or more additional vibration sensing units 10B. Such additional vibration sensing units 10B may be spaced apart along a single track, to provide improved accuracy. In some examples, the mounting location can be determined by track geometry. For example, if there are two different tracks merging, then the two tracks will both have an equivalent first vibration sensing unit 10A while the merged track with have a combined second vibration sensing unit 10B. In some examples, each of the unique sensor identifiers may be associated with one another. In some examples, the unique sensor identifier broadcast by the vibration sensing unit 10 may be identical to the unique detector identifier broadcast by the state detecting unit 20. The processing unit may be configured to verify the association by checking that the unique sensor identifier and the unique detector identifier are identical. In the case of one or more additional vibration sensing units 10B, in some examples the corresponding unique sensor identifiers may also be identical. Alternatively, in some embodiments the on-board computer 30 may be configured to look up one or both of the unique identifiers in a database 32 or lookup table, either stored locally or remotely from the on-board computer 30. The database 32 or lookup table may list each of the unique identifiers and include a record of any association between the unique identifiers. In this way, the on-board computer 30 may verify an association between non-identical identifiers. In some examples, the on-board computer 30 may be configured to scan for the broadcast detector data 201 in response to receiving the broadcast sensor data 101. In this way, the on- board computer 30 can save power by only scanning for the broadcast detector data 201 in response to a trigger. The on-board computer 30 can be triggered to scan once the received

9 MAIN\BOJOVI\39630035_1.docx 420626 sensor data 101 from the vibration sensing unit 10 indicates that the railway vehicle 4 is in the vicinity of the signal installation 2 and the state detecting unit 20. Alternatively, in some embodiments, the on-board computer 30 may scan for the broadcast sensor data 101 in response to receiving the broadcast detector data 201. In some examples, the output of the on-board computer 30 may include an identifier of the signal installation 2. In this way, the on-board computer 30 can indicate to the user, e.g. driver, exactly which signal installation 2 the detected state applies to, reducing the potential for confusion and driver error. Referring to Figure 1B, there is depicted a flowchart showing a representative process flow of the monitoring system 1 of Figure 1A. The first row 60 depicts an exemplary operation of the two vibration sensing units 10. The second row, 62 depicts an exemplary operation of the state detecting unit 20 mounted to the signal installation 2. The third row 64 depicts an exemplary operation of the on-board computer 30 on the railway vehicle 4. As described above, a train vibration is first detected above the first vibration sensing unit 10A. This results in a signal transmission, that is, the broadcast of the first sensor data 101A. After a short interval, a train vibration may be detected above the additional vibration sensing unit 10B. This may results in a signal transmission, that is, the broadcast of the additional sensor data 101B. The operation of the state detecting unit 20 may occur prior to, simultaneously with, or subsequently from the operation of the two vibration sensing units 10. The state detecting unit 20 receives visible light from the signal installation 2. As described in more detail below, the state detecting unit 20 may filter against ambient light. In addition, the state detecting unit 20 may apply a colour interpretation algorithm, e.g. to identify a red or green colour, also described in more detail below. The state detecting unit 20 is configured to broadcast the state indication of the signal installation 2 and a unique detector identifier. In some examples, the state indication may include the colour signal. As described above, the unique detector identifier may be associated with, or may be identical to, an ID of the signal installation 2. The on-board computer 30 is configured to receive the broadcast sensor data 101 and the broadcast detector data 201 and verify the association between the unique sensor identifiers and the unique detector identifier. The on-board computer 30 may look up a database record for the signal installation ID, corresponding to the unique detector identifier. A local or remote MAIN\BOJOVI\39630035_1.docx 420626 database 32 may include a record of an association between the signal installation 2 and the two vibration sensing units 10. The database record may include the unique sensor identifiers of the two vibration sensing units 10. In this way, the on-board computer 30 can verify the received unique sensor identifiers against the database record. The database record may further include an expected sequence of the two vibration sensing units 10. In this way, the on-board computer 30 can verify the sequence of the two vibration sensing units 10 against the database record. The combination of signals from the vibration sensing units 10 in the correct sequence and the signal from the state detecting unit 20 causes the processor 31 to trigger an alarm, alerting the operator of the train that the signal installation 2 has a particular state (e.g. a red-light state). This alarm may provide additional information about the signal state to the operator of the railway vehicle 4, with this information communicated to the operator using visual (e.g. an indicator light, dial, message on a display) haptic or auditory alerts. In some examples, the output may also include an indication of the signal installation ID. In some examples, the on-board computer 30 may be configured to output an alarm when there is an absence of a signal, e.g., the signal from the signal detecting unit. For example, the on- board computer 30 may output an alarm unless a signal from the state detecting unit 20 indicates that the signal installation 2 has certain state, e.g. a green-light state or any other colour state. In this way, the on-board computer 30 can provide a failsafe alarm in the event of a red light and/or a system/communication failure. Referring to Figure 2A, there is depicted a schematic representation of an exemplary vibration sensing unit 10. The vibration sensing unit 10 may include a vibration sensor 11, a processor 12, a transmitter 13, a battery 14, and a communication module 15. The vibration sensor 11 may be configured to provide a vibration level to the processor 12. In some examples, the vibration sensor 11 may be a 3-axis sensor, for example, a micro- electromechanical system (MEMS) device. The vibration sensor 11 may be sensitive up to 100G of acceleration. Alternatively, the vibration sensor 11 may be a single axis sensor e.g. a piezoelectric vibration sensor 11, or any suitable accelerometer. If the vibration level is larger than a certain threshold, the processor 12 is configured to broadcast a signal using the transmitter 13. In some examples, the vibration sensor 11 sensitivity may be adjusted by the processor 12. In this way, the vibration threshold can be set so that a wheel of the railway vehicle 4 must be on top of the sensor in order to trigger a MAIN\BOJOVI\39630035_1.docx 420626 response and other far away vibrations are not detected, thus avoiding incorrect wheel detections. In some examples, the processor 12 may control the transmitter 13 to broadcast once upon detection of the railway vehicle 4 and not broadcast again until the vibration level has passed below a predetermined threshold. In this way, power in the vibration sensing unit 10 can be conserved, and the vibration sensing unit 10 can prevent excessive broadcasting which may be received as noise by nearby railway vehicles, potentially causing confusing and/or erroneous alerts. In some examples, the processor 12 may be configured to put the vibration sensing unit 10 into a sleep state after a predetermined period of inactivity. In the sleep state an extremely low current drain occurs. The processor 12 may be configured to wake the vibration sensing unit 10 from the sleep state in response to a detected vibration level which exceeds a predetermined threshold. The transmitter 13 may be a radio transmitter, e.g., a chirp frequency radio transmitter. The transmitter 13 may be configured for short range transmission and high penetration ability. In this way, the broadcast data may reach a receiving device within a railway vehicle 4, e.g., an on- board computer 30. In some examples, the vibration sensing unit 10 may be configured to transmit the sensor data 101 using a high frequency chirp signal. The transmitter 13 may be configured to use a chirp frequency transmission that encodes the signal based on various parameters including any of frequency band, transmission power (penetration ability), spreading factor, bandwidth, coding rate, and/or packet size. Some or all of these parameters may be optimized, for example, so that signals exceeding 1 car distance are not detected in range. In this way, other trains can be prevented from receiving the signal. In some examples, the transmitter 13 can be adjusted to use various frequencies such as 920MHz for Asia/Hong Kong, 868 MHz for USA, and 433MHz for generic bands or EU. The battery 14 may be an internal battery or an externally connected battery pack. In some examples, the battery 14 may be configured to last more than 1 year. The communication module 15 may include a wired or wireless communication means. For example, the communication module 15 may be configured to communicate using any of USB, Ethernet, Bluetooth, Near-field communication (NFC), mobile internet (e.g.4G or 5G), Wi-Fi or any other appropriate communication mode. In some examples, the communication module 15 may be integrated with the transmitter 13. MAIN\BOJOVI\39630035_1.docx 420626 The communication module 15 may be configured to interface with the processor 12 in order to configure the vibration sensing unit 10. For example, the vibration sensor 11 sensitivity may be adjusted by a user via the communication module 15, e.g., by using Bluetooth to communicate with the vibration sensing unit 10 via mobile phone or laptop or by connecting remotely via an web-based app. In some examples, the unique sensor identifier may be programmable via the communication module 15. In some embodiments, the vibration sensing unit 10 can be provided independently of the monitoring system 1 described above. In this way, the vibration sensing unit 10 can provide a standalone means of detecting the presence of a railway vehicle 4 at a specific location and transmitting a signal to indicate that location to one or more devices inside the railway vehicle 4. In comparison with conventional solutions, e.g. a balise, the vibration sensing unit 10 is lightweight, low cost and low power. It can provide a fully modular solution because the unit can be battery powered for an extended period of time, so no wired connection is required. As such, the vibration sensing unit 10 can simply be clamped on to the railway track 3 at any desired location, as described in more detail below. Referring to Figure 2B, there is depicted a perspective view of an exemplary vibration sensing unit 10 mounted to a railway track 3. As shown, the vibration sensing unit 10 may include a housing 16, a first clamping part 17 and a second clamping part 18. The housing 16 is configured to contain each of the functional components described with respect to Figure 2A. In some examples, the housing 16 may contain one or more batteries. In some examples, as shown, the vibration sensing unit 10 may be connected to one or more batteries disposed near to the housing 16 of the vibration sensing unit 10. The housing 16 is configured to be sealed and weathertight for outdoor use. One or more external ports e.g. for connecting to the communication module 15 or connecting the battery 14, may be protected by seals to prevent ingress of water. The housing 16 may be coupled to the first clamping part 17. The first clamping part 17 is shaped so as to engage with a corresponding first side of the railway track 3. As shown, where the railway track 3 has an I-beam construction, the first clamping part 17 may be shaped to engage with a lower flange of the I-beam, in order to support the housing 16 in a position below the wheels and chassis (or bogie) of a passing railway vehicle 4. The first clamping part 17 may be approximately C-shaped, with an inner surface shaped to engage with the railway track 3. The shape of the inner surface may be closely matched to the shape of the railway track 3 such that the inner surface is predominantly in directed contact with the railway track 3. In this way, MAIN\BOJOVI\39630035_1.docx 420626 the first clamping part 17 is able to transmit vibrations in the railway track 3 fully to the vibration sensor 11 in the housing 16. The second clamping part 18 is shaped so as to engage with a corresponding second side of the railway track 3, opposite to the first clamping part 17. The second clamping part 18 is configured to engage with the first clamping part 17 to compress the railway track 3 therebetween. The second clamping part 18 may be approximately C-shaped, with an inner surface shaped to engage with the railway track 3. The shape of the inner surface may be closely matched to the shape of the railway track 3 such that the inner surface is predominantly in directed contact with the railway track 3. Referring to Figure 2C, there is depicted a cross sectional view of a railway track 3 to which an exemplary railway sensor has been mounted. As shown, the second clamping part 18 comprises one or more bolts arranged to pass through the second clamping part 18 and engage with the first clamping part 17. The bolts may be threaded bolts configured to engage with a thread in the first clamping part 17 or with a threaded nut. In some examples, the second clamping part 18 may include 4 bolts. In some examples, one or more bolts may be arranged to pass through the first clamping part 17 to engage with the second clamping part 18. In this way, the vibration sensing unit 10 can be mounted to the railway track 3 with sufficient rigidity and clamping strength to fully transmit vibrations in the track to the housing 16. Referring to Figure 3, there is depicted a schematic representation of an exemplary state detection unit. The state detection unit may include a light sensor 21, a processor 22, a transmitter 23, a battery 24 and a communication module 25. The light sensor 21 is configured to output light sensor data. In some examples, the light sensor 21 may be a red-green-blue (RGB) light sensor configured to output RGB data. The light sensor 21 may be arranged in proximity to the signal installation 2 to receive light from the signal installation 2. For example, where the signal installation 2 is a traffic light, the RGB sensor may be arranged in proximity to one of the lights, e.g. the red light. In this way, the state detecting unit 20 can detect the state of the signal installation 2 without any modification to the signal system. In some examples, the state detecting unit 20 may be encapsulated in silicone and quartz crystal glass. This can improve optical visualization of the traffic light by the light sensor 21 and allows the enclosure to be waterproofed to ensure it can work under rain conditions. MAIN\BOJOVI\39630035_1.docx 420626 As shown in Figure 1A, the light sensor 21 may be mounted to directly to a screen of the red light, to receive the emitted light. In some examples the light sensor 21 may be mounted to the red light using adhesive. The light sensor 21 may be configured to have a small package size, in comparison with the light of the signal installation 2. In some examples, the light sensor 21 may be connected with the processor 22 and/or other components of the state detecting unit 20 via a wire, in order to reduce the size of the package mounted to the red light. In this way, the state detecting unit 20 can receive visible light from the signal installation 2 without hindering the overall visibility of the signal emitted by the signal installation 2 for the driver. In addition, the state detecting unit 20 does not require any structural or electrical modification to the signal installation 2. A package enclosing at least the processor 22 and transmitter 23 of the state detecting unit 20 may be referred to as a transmission link module 26. The transmission link module 26 may be wire connected to the light sensor 21 using a wire. In some examples, the transmission link module 26 may be mounted to the signal installation 2 using a metal clamp so that no structural holes need to be drilled. In some examples, the state detecting unit 20 may include a plurality of light sensors 21, for example, the state detecting unit 20 may include a separate light sensor 21 for each light of a traffic light signal installation 2. In some examples, the light sensor 21 may include one or more monochromatic light sensors, for which the indication of state is based on knowledge of the sensor position. For example, a red-light state can be indicated by a positive signal from the light sensor 21 which is known to be positioned adjacent to the red light. The processor 22 is configured to receive the light sensor data from the light sensor 21, and control the transmitter 23 to broadcast detector data 201 including a state indication of the signal installation 2. In some examples, the state indication may include the light sensor data. In some examples, the processor 22 may be configured to determine the state of the signal installation 2. The state indication broadcast by the transmitter 23 may include a determined state of the signal application. In some examples, the processor 22 may be configured to determine the state using an algorithm based on the RGB data. The RGB data may include intensity levels for each colour, i.e. red, green and blue. The processor 22 may be configured to translate the colour intensity levels into a brightness level and a colour temperature level. MAIN\BOJOVI\39630035_1.docx 420626 The processor 22 may be configured to determine whether the state of the signal installation is a red-light state by applying thresholds to each of the three parameters: RGB light intensity, brightness and colour temperature. In some examples, this approach may be used to determine any other state, e.g. an amber-light state or any other colour, by adjusting the thresholds appropriately. In some examples, a threshold may be used on one or more of the parameters (RGB light intensity, brightness, and colour temperature) to filter out ambient light. In this way, the processor 22 can filter out high ambient light, allowing the state detecting unit 20 to operate in outdoor areas with high ambient light. In some examples, the state detecting unit 20 may be configured to broadcast the detector data 201 based on the determined state. For example, the processor 22 may be configured to control the transmitter 23 to broadcast the detector data 201 only in response to determining that the state of the signal installation 2 is a red-light state. In this way, the state detecting unit 20 can prevent broadcasting when the state is not a particular state of interest, e.g., a red-light state, thus reducing power consumption of the state detecting unit 20. In some examples, the processor 22 may be configured to put the state detecting unit 20 into a sleep state. In the sleep state and extremely low current drain occurs. In some examples, the processor 22 sleeps and wakes up for a few milliseconds at predetermined intervals to check the output from the light sensor 21. The transmitter 23 may be a radio transmitter, e.g., a chirp frequency radio transmitter. The transmitter 23 may be configured for relatively long-range transmission, in comparison with the transmitter 13 of the vibration sensing unit 10. In this way, the broadcast data may reach a nearby railway vehicle 4. In some examples, the state detecting unit 20 may be configured to transmit the detector data 201 using a high frequency chirp signal. The transmitter 23 may be configured to use a chirp frequency transmission that encodes the signal based on various parameters including any of frequency band, transmission power (penetration ability), spreading factor, bandwidth, coding rate, and/or packet size. Some or all of these parameters may be optimized, for example, so that signals can transmit a relatively long distance to the train location and the distance can be adjusted by transmission power. The battery 24 may be an internal battery or an externally connected battery pack. In some examples, the battery 24 may be configured to last more than 1 year. The communication module 25 may be configured to interface with the processor 22 in order to configure the state detecting unit 20. For example, the light sensor sensitivity may be adjusted MAIN\BOJOVI\39630035_1.docx 420626 by a user via the communication module 25, e.g., by using Bluetooth to communicate with the state detecting unit 20 via mobile phone or laptop or by connecting remotely via an web-based app. In some examples, the unique detector identifier may be programmable via the communication module 25. In some embodiments, the state detecting unit 20 can be provided independently of the monitoring system 1 described above. In this way, the state detecting unit 20 can provide a standalone means of detecting the state of a signal installation 2 and transmitting a signal to indicate that state without any modification of the signal installation 2 or related infrastructure. The state detecting unit 20 is lightweight, low cost and low power. It can provide a fully modular solution because the unit can be battery powered for an extended period of time, so no wired connection is required. As such, the state detecting unit 20 can simply be adhered to a signal installation 2 at any desired location, as described in more detail below. Referring to Figure 4, there is depicted an exemplary schematic view of a computing device 100 used on board the railway vehicle in accordance with one embodiment. Device 100 can be a client computer or a server unit which is assessed to meet the reliability and redundancy requirements for operation in railway networks. The computer may include a transmitter with, for example, 3 radio channels. The computer may be configured to have a fast boot rate of, e.g., a few milliseconds. The computer may use a real time operating system. The computer may be configured to connect to an on-board power supply on the train, e.g. a 110V power supply. Device 100 can be any suitable type of microprocessor-based device, most likely a computer, workstation, server but optionally a handheld computing device (portable electronic device) such as a phone or tablet. The device 100 can include, for example, one or more of processor 110, input device 120, output device 130, storage media 140, and communication interface 160. Input device 120 and output device 130 may be connectable or integrated with the computer. Input device 120 can be any suitable device that provides input, such as a touch screen, keyboard or keypad, mouse, or voice-recognition device. In some examples, input device 120 may be provided by a separate device, e.g. a mobile device configured to communicate with the device 100 via Bluetooth. Alternatively, user instructions may be provided as text commands, e.g. stored in an SD card, and the input device 120 may be omitted. Output device 130 can be any suitable device that provides output, such as a touch screen, haptics device, or speaker. MAIN\BOJOVI\39630035_1.docx 420626 Storage 140 can be electrical, magnetic or optical memory including a RAM, cache, hard drive, or removable storage disk e.g. an SD card. In some examples, the storage 140 may store one or more audio files for playback by the output device 130. In some examples, the storage 140 may store one or more user instructions e.g. to adjust the software parameters or processor settings. Communication interface 160 can include any suitable device capable of transmitting and receiving signals over a network. The components of the computer can be connected in any suitable manner, such as via a physical bus or wirelessly. Software 150, which can be stored in storage 140 and executed by processor 110, can include, for example, programming that embodies the functionality of the present disclosure (e.g., as embodied in the devices as described above). Alternatively, processor 110 may include a microprocessor with built-in memory to store the software 150. Software 150 can also be stored and/or transported within any non-transitory computer- readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as those described above, that can fetch instructions associated with the software from the instruction execution system, apparatus, or device and execute the instructions. In the context of this disclosure, a computer-readable storage medium can be any medium, such as storage 840, that can contain or store programming for use by or in connection with an instruction execution system, apparatus, or device. Software 150 can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as those described above, that can fetch instructions associated with the software from the instruction execution system, apparatus, or device and execute the instructions. In the context of this disclosure, a transport medium can be any medium that can communicate, propagate or transport programming for use by or in connection with an instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. Device 100 may be connected to a network, which can be any suitable type of interconnected communication system. The network can implement any suitable communications protocol and can be secured by any suitable security protocol. The network can comprise network links of any suitable arrangement that can implement the transmission and reception of network signals, in operation, especially wireless network connections, but may also include wired connections. Device 100 can implement any operating system suitable for operating on the network. Software 150 can be written in any suitable programming language, such as C, C++, Java or MAIN\BOJOVI\39630035_1.docx 420626 Python. In various embodiments, application software embodying the functionality of the present disclosure can be deployed in different configurations without departing from the scope of the present disclosure. Referring to Figure 5, there is depicted a flowchart of an exemplary method of an embodiment of the present disclosure. The method starts at step S11. At step S12, the method comprises detecting, using a vibration sensing unit engaged with a railway track at a location proximate to the signal installation, a railway vehicle moving upon the railway track proximate to the vibration sensing unit. At step S13, the method comprises broadcasting, by the vibration sensing unit upon detection of the railway vehicle, broadcast sensor data including a unique sensor identifier; At step S14, the method comprises receiving visible light emitted from the signal installation using a state detecting unit engaged with the signal installation; At step S15, the method comprises broadcasting, by the state detecting unit, detector data including a state indication of the signal installation and a unique detector identifier, wherein the unique detector identifier is associated with the unique sensor identifier; At step S16, the method comprises receiving the broadcast sensor data and the broadcast detector data using an on-board computer disposed in the railway vehicle; At step S17, the method comprises verifying, by the on-board computer, the association between the unique sensor identifier and the unique detector identifier; and At step S18, the method comprises outputting, by the on-board computer, the state of the signal installation if the association is verified. The method ends at step S19. The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the disclosure as defined in the appended claims. For clarity of explanation, in some instances the present technology may be presented as including individual functional blocks including functional blocks comprising devices, device components, steps or routines in a method embodied in software, or combinations of hardware and software. MAIN\BOJOVI\39630035_1.docx 420626 Methods according to the above-described examples can be implemented using computer- executable instructions that are stored or otherwise available from computer readable media. Such instructions can comprise, for example, instructions and data which cause or otherwise configure a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Portions of computer resources used can be accessible over a network. The computer executable instructions may be, for example, binaries, intermediate format instructions such as assembly language, firmware, or source code. Examples of computer-readable media that may be used to store instructions, information used, and/or information created during methods according to described examples include magnetic or optical disks, flash memory, Universal Serial Bus (USB) devices provided with non-volatile memory, networked storage devices, and so on. Devices implementing methods according to these disclosures can comprise hardware, firmware and/or software, and can take any of a variety of form factors. Typical examples of such form factors include laptops, smart phones, small form factor personal computers, personal digital assistants, and so on. Functionality described herein also can be embodied in peripherals or add-in cards. Such functionality can also be implemented on a circuit board among different chips or different processes executing in a single device, by way of further example. The instructions, media for conveying such instructions, computing resources for executing them, and other structures for supporting such computing resources are means for providing the functions described in these disclosures. Although a variety of examples and other information was used to explain aspects within the scope of the appended claims, no limitation of the claims should be implied based on particular features or arrangements in such examples, as one of ordinary skill would be able to use these examples to derive a wide variety of implementations. Further and although some subject matter may have been described in language specific to examples of structural features and/or method steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to these described features or acts. For example, such functionality can be distributed differently or performed in components other than those identified herein. Rather, the described features and steps are disclosed as examples of components of systems and methods within the scope of the appended claims. MAIN\BOJOVI\39630035_1.docx 420626