1. Field of the Invention
The present invention relates to printed indicia and, more particularly, to a hidden fluorescent indicium.
2. Brief Description of Prior Developments
In some applications, indicia such as one dimensional or two dimensional bar codes are printed on the items, such as mail pieces. For example, bar codes are often used on a mail piece such as with or in postage meter indicia. A black color is preferably used for printing two dimensional bar codes and is the preferred color for optimal contrast and readability. One problem with the printing of black two dimensional bar codes is that they can lead to easy duplication by available desktop printers or copiers. The black prints can easily be copied by any black-and-white copier or scanned and reprinted easily by available printers. Another problem is that everyone can see what is printed in the bar code. In some applications it is desirable to pass some information covertly. Dark color fluorescent inks are known such as described in U.S. patent application publication Nos. US 2002/0195586 A1, US 2003/0005303 A1, and US 2003/0041774 A1, which are hereby incorporated by reference in their entireties.
There is a desire to hide information in a printed indicium, but which can be relatively easily verified or read. There is a desire to provide hidden information which can be used to provide an additional level of security, such as with postage indicia.