Here at Harlan Berk's coin store in downtown Chicago, it is not unusual to see $50 and $100 bills with small rubber stamps on them. They are presumably bankers' and money exchangers' marks from overseas, indicating that the bank or exchanger in question has examined the note and found it to be genuine. It is the equivalent of the Chinese chop mark on 19th century crown-sized coins such as Trade Dollars. We just ignore them, and use our own observations of official counterfeit detection devices on the bills to verify them. After all, any counterfeiter could put any variety of "chop marks" on his bills to make it easier to pass them.

The "M" in the star of David on the $50 note is a money-changer's chop mark. Hundreds exist - so that the money-changer will not have to examine the note closely the next time he receives it, to determine its authenticity. Such marks are widely used in the mid-east, somewhat less in the far east.