Welcome to the forum.
Mike, not to disagree, but the 1921 would be a date stamp, only the 1920 was a property stamp, and the acceptance and proofs on the right are consistent with a 1921. Like Mike said, it is a 5 digit commercial that was then placed into military service.
The unit marking is a Weimar one, as Mike said
In addition the rear number is likely a unit rack number, that is the common belief and one I believe is true.
Value if all matching is about $800-$1000? Perhaps more if someone was looking for this marking, but its condition is not pristine (nice, but not pristine).
Ed