First U.S. Stamp with Scrambled Indicia
On September 18, 1997, the USPS issued the U.S. Air Force stamp, the first U.S. stamp to have a hidden image using Scrambled Indicia.
Over the years, the USPS had always sought ways to combat counterfeiting, with grills being one of the earliest examples. As technologies changed, they found new, more advanced ways to do this, including microprinting and tagging. Then in 1997, they introduced Scrambled Indicia.