a fade resistant , visually undetectable identification mark is imparted to an optically clear plastic lens or the like by providing a marking composition comprising a fluorescent dye and a liquid carrier material , and preferably including an inert sublimable solid diluent , applying the composition in a selected pattern on the surface of an article to be marked , removing the carrier material from the composition to leave a solid residue of the fluorescent dye and inert solid diluent , and permanently transferring the dye to a surface layer of the article as by heating . the mark enables a manufacturer to identify a particular article as its product by exposing it to ultraviolet radiation , yet the mark does not adversely affect the visible light optical properties of the article .