Dri Mark Smart Money Counterfeit Detector Pen with Reusable UV LED Light (DRI351UVB) Double your capabilities. Powerful LED with reusable ultraviolet light cap makes it easy to check UV security threads. Highly effective on U.S. and foreign currencies, passports, cashier's checks and money orders. Chemically sensitive ink enables quick and easy currency tests. An amber mark passes, whereas a dark brown or black mark fails.