Dri Mark Counterfeit Detector Pen with Holder and Coil (351BCL) The original and best Counterfeit Detector Pen, patented by Dri Mark in 1991. Comes with an adhesive holder and coil tether to keep your Counterfeit Detector right at the register. A simple mark on paper currency: dark mark means counterfeit, light mark passes test The only Counterfeit Detector Pen still made in the USA Superior quality means superior performance