A method of providing secure identification for an article, including: providing on the article a diffraction grating strip including a pattern of a series of diffraction grating elements, each the diffraction grating element to diffract light, from a light source, in one of at least three selected...http://www.google.de/patents/US5841555?utm_source=gb-gplus-sharePatent US5841555 - Secure optical identification method and means
