US Patent 7422158 Fluorescent hidden indicium

A printed indicium including a first section and a second section. The first section includes a first ink having a first color under normal daylight. The second section includes a second different ink. The second ink includes a fluorescent ink which has a second color under normal daylight which is substantially the same as the first color. The fluorescent ink has a fluorescence when subjected to fluorescent-exciting radiation. The second section is imbedded with the first section such that the first and second sections are substantially visually indiscernible from each other in normal daylight.