Here are images of the reverse of a $100 2003 series A note. This is the first time I've seen something like this....has this note possibly been across the water? These stamps remind me of chopmarks on coins.

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.

Because there are so many counterfeit $100 'super notes' in circulation, merchants and foreign money exchangers in Southeast Asia are chopping all they consider authentic. The practice is quite common and it's now unusual for me to find $100 notes without them in Southeast Asia.