Well, an army gun would also be marked on the left side.
Some kind of a put together mix master, post war; but which war is uncertain.
Although everyone says that it must have a serial nubmer, it was not till I think 1968 before that was required....
So, I would guess you'd talk your way into it being registered as one of the numbers on the left, the 1916 or the DWM...
There are better guns to buy unless it is a real steal in price
Ed