IMPROVEMENTS IN OR RELATING TO SECURITY OR AUTHENTICATION MARKINGS AND THE LIKE

摘要

A security or authentication marking on a document or product takes the form of refractive index variations or other variations in light managing properties, in a layer or sheet of light-transmitting material provided on or in at least part of the document or product. The light-transmitting material may be in the form of a sheet of said light-transmitting material extended over a light-transmitting aperture or window in the document or product, or may be extended in a layer across a light-transmitting part of the product, or over a light-reflecting part of said document or product.