This invention relates to a method and apparatus for security marking articles having a plastics outer surface, and in particular to a method and apparatus suitable for security marking articles having a plastics outer surface, whilst in in situ in a vehicle.

U.K. patent specification 2145036 discloses apparatus for hot foil embossing which has a head arranged to receive an array of embossing type faces. Such apparatus can be used to mark a flat accessible surface but is however of little use in marking oddly shaped articles, or where articles are relatively inaccessible and small portions thereof need to be accurately marked as is often the case where articles are fitted in the interior of a vehicle.

According to a first aspect of the invention, there is provided a method of security marking, in situ in the interior of a vehicle, an article at least a portion of the surface of which is of a plastics material, the method comprising thermally deforming said portion of said surface so as to leave at least one recessed visible indicium thereon, said indicium being indicative of a characteristic of said vehicle.

It is preferred that at least one indicium is indicative of at least two independent characteristics of the vehicle.

Typically, the article may be, for example, a car cassette player, radio, compact disc player or the like having a plastics outer housing.

It is preferred that the thermal deformation of the portion of the surface is achieved by the application of a heated member.

In a preferred embodiment, the heated member is applied to the surface of the article with a sheet of metallic foil interposed therebetween. The foil sheet preferably has a melting point at or below the temperature of the heated member. When the heated member is applied to the portion of the article surface with the foil sheet interposed therebetween, the metallic foil conducts the heat from the heated member to the plastics portion of the outer surface which deforms as a result leaving a recess, leaving the foil adhered to and within the recess, in a similar manner to the known hot foil printing process.

Advantageously, the foil-contacting portion of the heated member may be shaped to produce a correspondingly shaped recess which shaped recess may then constitute the indicium.

It is preferred that the indicium is in the form of an alphanumeric character, such as a digit, or more preferably a letter of the alphabet. Such a letter may represent a letter (such as a prefix) from the vehicle's registration number which indicates the year of manufacture of the vehicle (a first characteristic).

It is further preferred that the metallic foil sheet is coloured such that when solidified in the recess an identifiable colour is visible.

This colour may be used to characterise the "make" of a particular car by the use of a "colour coding" system. For example red may represent a Vauxhall vehicle, yellow a Renault and so on (a second characteristic of the vehicle).

An article security marked in this way will thus be identifiable as associated with a particular "make" and year of manufacture of vehicle. As such the article should be less attractive to would be thieves and easily recognisable as stolen if present in a vehicle of "different" make and age.

According to a second aspect of the invention, there is provided apparatus for security marking an article, at least a portion of the surface of which article is of a plastics material, which apparatus comprises a die element having projecting from a surface thereof a formed representation of at least one indicium, said die element being arranged to be removably received and retained in heat conducting housing means provided at a proximal end of an elongate heat transfer member, the distal end of said heat transfer member being connected to an elongate insulating handle member, which handle member is remote from said proximal end of said elongate heat transfer member, and contains heat generation means arranged such that when said die element is retained in said housing means it can selectively bring said die element to an elevated temperature by means of heat conduction from said heat generating means via said elongate heat transfer member and said housing means to said die element.

Manipulation of the handle by the user enables the orientation of the die element to be altered such that the desired portion of the article may be marked. It is particularly important that the elongate heat transfer member is provided since this enables oddly shaped articles or otherwise inaccessible articles to be marked effectively.

It is particularly preferred that the longitudinal axes of the elongate heat transfer member and the handle member are substantially parallel, and more preferably co¬ axial, to facilitate ease of marking.

Advantageously, the transverse cross sectional area of at least a part of the elongate heat transfer member, and also preferably the transverse cross sectional area of the housing mens, is less than the greatest transverse cross sectional area of the handle member. The apparatus can thereby be used in the manner of a probe and accurately mark inaccessible or oddly shaped articles.

Advantageously, the housing means is arranged to locate and retain the die element only in one orientation relative to the transverse direction of the elongate heat transfer member. Advantageously, the said one orientation of the die element lies on the longitudinal axis of the heat transfer member, and also advantageously on the longitudinal axis of the handle means.

The die element may advantageously, be a member of a set comprising a plurality of die elements, each being selectively retainable in said housing mens and having, projecting from a surface thereof, a representation of a different indicium.

It is preferred that the heat generation means is electrically operated; more preferably the heating means is in the form of an electrical resistance heating device provided in the handle means.

Preferably the heat generation means is electrically connectable to a power supply remote from the apparatus.

The die element is removable from the housing means enabling a replacement die element to be inserted therein.

Advantageously the die element, heat transfer member and housing means are of a metallic material, this may be a copper alloy such as brass or the like.

The invention will now be further described in a specific embodiment, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an exploded perspective view of a security marking device according to the invention; and

Figure 2 is a schematic representation of an article security marked in accordance with the invention.

Referring to the drawings, the security marking device, generally designated

1 has at one end an elongate insulating plastics handle 2 having a protective collar 11. Extending longitudinally out of the handle 2 is an elongate metal arm 3 which is provided at the end remote from the handle 2, with a housing socket portion 4 shaped to receive therein a complementary shaped brass die element 5. A threaded grub screw 6 is located through the wall of the housing socket portion 4 such that the die element 5 may be releasably retained securely therein.

The brass die element 5 has a front surface 7 with an indicium character (in this case the letter A) standing proud thereof.

Electrical power is supplied to a heating element (not shown) within the handle

2 via a cable 8 connected to a variable power supply (not shown) which produces a constant output of 4 amps at 65 volts.

Heat is conducted from the heating element along the metal arm 3 and into the abutting brass element 5 which becomes "hot".

In use, this hot die element is pressed into the plastics surface of an article (in this case the plastics facia 10 of a car stereo player) whilst a coloured metallic foil sheet 9 is positioned therebetween.

The heat of the die 5 causes the plastics surface of the article to deform and produce a recess in the shape of the indicium character present on the die surface 7 (the letter A in Figure 2). The heat of the die also causes the portion of the colour metal foil in contact with the character A to adhere to the plastics surface within the recess A.

As a result, a recessed indicium is created on the surface of the article which being of a characteristic shape and colour, can convey items of information about the vehicle. The particular letter used (in this case A) corresponds to the registration date letter (prefix letter) of the vehicle and the colour of the letter to the "make" of vehicle, e.g. yellow for Renaults, red for Vauxhall etc.

If a security marked cassette player was stolen for example from an A registration Renault the indicia would be an impressed A mark coloured yellow. If such a stolen cassette player or the like were present in a vehicle of different age or "make" it would be easily identified as stolen.

Since the indicium mark A is recessed, it is extremely difficult to remove without defacing (and hence devaluing) the article it is applied to. Furthermore, as the security marking device is hand held and portable the device can be used to security mark articles such as car radios, cassette players and compact disc players whilst they are in situ in a vehicle. To this end it is important that the handle 2 and metal heat conductive arm 3 are co-axial and also that the die 5 is retained on the longitudinal axis of the handle 2 and arm 3, since this enables accurate positioning of the die, and hence marking of the article, when the article is oddly shaped or in accessible (such as is the case when a car radio is in position in a vehicle) and care must be taken not to accidentally heat or deform other heat deformable or heat sensitive surfaces in the vicinity of the article being marked.