I use a stamp on my one dollar notes that reads "Postage rates are too high". Kind of like "Where's George" notes. Just my little jab at the USPS. Can't use it on mail otherwise it would get lost magically. I do strange things every now and then.
All types of rubber stamps have been used on paper currency and this is just one of them. NAV, spend it.
There is probably no way to ever determine the “owner” of the various “chop marks”. But they are fun to collect. I take pictures of them and return the bills to circulation. That is primarily because I find most of them on $100 bills. I have about 12 different ones now. I only started collecting them about 6 months ago.