I am interested to know how large of a real problem this is. In my 64 years in the USA, I have never seen or been passed a counterfeit bill. In 12 years of owning a home in Argentina, and conducting most of my business in cash, my wife and I saw ONE counterfeit 100 peso bill. She got it exchanged for a good one, as I remember. So my total lifetime loss due to counterfeits is far below the cost of a magic pen. YMMV.