Butt stamp question...

[Don M]

Mark, et al.,
I am continuing to learn more about these police unit marks and will add a further speculation about the original mark. It may have been: S.Op.?.7.109., where the ? was a Roman numeral. This format was specified by the 1922 Prussian marking order where the ? represents the Abteilung (Department), later Inspektion (Inspectorate); 7 represents the Hundertschaft, later Bereitschaft (riot squad); and 109 is the weapon number within Hundertschaft 7. The 1932 Manual 40a revised and simplified this format for the Schupo. The new format was S.X.Y.xxx., where X was the abbreviation for the Prussian Regierungsbezirk (Administrative District), Y an optional Roman numeral indicating the Inspectorate for districts having more than one, and xxx. the weapon number within that Inspectorate.

From the photo in the thread starter, it appears that the earlier ?.7.109. was partially ground off and overstamped with IV.221., consistent with the 1932 instructions.

I find these multiple marks fascinating!