I got a few US $100 notes from a guy from Philippines. I noticed they had been counter-stamped with various logos, probably of banks which authenticated the notes. These logos are just like the old chop mark silver coins. I have never seen them in USA, but then the US $100 hardly circulates in USA, and this must be a far East phenomena..

What is the Numismatic term for them. . . ? I could not find a write up about them on the Internet.

I was told by a currency dealer that with the mark, that agency will accept back the note if found to be a forgery. But then the mark also may get forged to make them more acceptable.

I call these chopmarks, as do most other paper collectors. I have them from both the far east and mideast (Arabic script chops). They are used so that a moneychanger does not have to study a note closely, if it already has his chop showing that he did that before. Sure, they could be forged, but the original user would be quite likely to detect that easily - it's not likely to be a perfect match for the stamp he has on his desk. As far as I know, nobody has studied these, and certainly no guide exists linking each chop to its originating source. A friend here in Indianapolis is trying to build an exhibit of these for US competition at coin shows. I don't know how many he has collected, nor what approach to describing them he plans to take.