4506916 A abstract a card is disclosed which is made of a thermoplastic material and having visually recognizable internal safety markings the card comprises a first sheet of a transparent thermoplastic material and a second sheet of an opaque thermoplastic material the second sheet has an inner surface provided with a relief structure such that the varying thickness of the opaque material will influence the local absorption of transmitted light the first sheet has an inner surface provided with a corresponding negative relief structure the first and second sheets are laminated together with their inner faces in contact to form an interface thus when viewing the card in transmitted light the relief structure is visually recognizable as a varying brightness due to varying absorption of the light transmitted through the opaque sheet application_number US 35054082 A description although the following description refers to the already mentioned various embodiments of which one refers to a marking when viewing through the card and the other to a marking when simply the card from above are shown separately from each other it must be mentioned that this separate description of those two procedures is for clarity 39 s sake only and that both.