Trapdoor Rifles

How often does one encounter Trapdoors (both 50/70 and 45/70), where the "U.S." stampings have been intentionally and crudely removed?

I don't recall ever seeing any trapdoors with U.S. obliterated.
Later stuff like single action armies, M1911s are a different story.

But, I have not seen them all.

A number of trapdoor rifles have been seen with the U.S. on the block, the U on the springs and the U.S. on the lock crudely removed. These guns were sold to the public and to Indian reservations so as to not be claimed as US issue and not get in trouble with the government. Buffington was really mad about people assembling and selling trapdoor rifles altered in this way and also stamping false cartouches and firing proofs on assembled guns. Some of these guns are in the Springfield museum.

Or the one with the serial number removed with a file. Seems someone thought they could be traced to an individual or unit.

Look in Book II on pages 314 and 315 for an example of one of these "commercial" trapdoors.