Big fan of the Forum, very informative site!

So, I have bought a deactivated Thompson 1928A1, fixed Lyman sights, very happy..Sad not to be able to shoot it, but there we go..

The serial number is S-397513. I’m guessing it was made by Savage, around April of 1942..

can anyone tell me what the marking here shown mean? Are these lease lend/ Russian stamps? Proof marks?

Any ideas/ information appreciated,

Have a good day

Jon MB