PURPOSE: To prevent any pertinent identification from being hampered due to individual difference of workers, extent of fatigue, etc., by a method wherein a defective print identification mark is printed together with letters, codes, marks, etc., as necessary to identify the acceptability of light and shade as well as accurate positions of printing.

CONSTITUTION: A defective print identification mark 1 is composed of a mark component part 2 with total height of mark 1 located on the central part of mark 1 in the width direction and provided with a narrow part 2a as well as multiple mark component parts 3 comprising an upper and lower pair of subparts located on both sides of the component part 2 with respective gaps diminishing the height thereof. When the printing is too thick, the overall mark 1 is printed continuously due to the gaps filled with ink but when the printing is moderate, the gaps between respective component parts as well as both end of component parts are clearly printed while when the printing is too thin, both ends of the defectie printed identification mark 1 as well as the component part nearby are not clearly printed.