"Heat Sensitive Camouflaged Message"
U.S. Patent 5,873,604 - 6,396,927 - 5,636,874
G.B. Patent 2,276,588 B
Brisk and rapid rubbing of the indicia areas reveals a hidden valid alert message and verifies authenticity. Additionally, the heat from a color copier will normally activate the hidden alert message causing the accepting party to read the warning message. The activated message reverts back to its camouflaged effect upon cooling.