Bank Marks On Currency?

These are stamped on notes by money changers, casinos, banks etc. Most of them are done overseas. And frankly they can be a pain if you go anywhere where they will not take bills so marked. A few years ago I traveled to Ukraine, and Poland and had to accumulate a sizable amount of cash since credit cards are still not common there. The big pain of it was that you have to have unmarked, and not worn bills. And try to find enough of them.

The absolute worst as far as accepting currency was the US Embassy in Warsaw Poland, they even have a machine that checks them.

It is common to require cashiers to mark the bills they accept so if a counterfeit was accepted, they know which employee to "Retrain".