What kind of marker pens do banks use to check for fake money?

Answer 1

The Patented Smart Money® Counterfeit Detector Pen has revolutionized counterfeit detection. Dri Mark's Counterfeit Detector pen is a highly effective and inexpensive tool for detecting bad bills and deterring counterfeiters from passing phony currency in the first place. Simply make a small mark on U.S. currency. An amber mark passes the test, 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). Made in the USA.

Answer 2

They are special pens you get at a business supply store.