Highly effective and inexpensive tool for detecting bad bills. Simply make a small mark on U.S. currency. Chemically sensitive ink works instantly. An amber mark passes the test, while a dark brown or black mark means the bill is probably counterfeit. Works on all new design U.S. currency bills series 1959 and later. Counterfeit Bill Detector Type: Pen Marking Color: Amber Counterfeit Indication Mark: Black Dark Brown Currency: U.S.