German law requires that every gun that enters the country and does not already bear a recognized civil proof marking (a military acceptance mark is NOT sufficient)* must be proofed and marked by a recognized proof house, with the proof marks being applied to barrel, receiver and bolt, also marked with the date (may be coded) and name or recognized mark of the importer. Also caliber if not already marked.
*No, not even if it's a Mauser that was originally made in Germany!