In a preferred embodiment, a method of providing secure identification for an article, including: providing on the article a diffraction grating strip comprising a pattern of a series of diffraction grating elements, each of the diffraction grating elements to diffract light, from a light source, in...http://www.google.de/patents/US6560017?utm_source=gb-gplus-sharePatent US6560017 - Compound secure optical identification method and means
