Abstract: A non-embossed security foil formed by a first taggant and a second taggant each positioned on a metallic surface and optically reactive to different stimuli for confirming the authenticity of important documents is provided. Each taggant defines a different color when exposed to an associated optical stimulus such as an infrared (IR) laser pen, allowing for the creation of multiple color, in register indicia or images that are covertly embedded into official documents and which are otherwise invisible to the naked eye. A method of utilizing taggants that are optically reactive to stimuli of different wavelengths is also provided.