Pete, thanks for looking up the link.
Bob,
I'm going to offer a somewhat different interpretation of these marks. I'm posting an edited version of your earlier photo:
First, let me say that I think that all three marks are from the same unit, despite the differences. While it is possible that S.S. means Schutzpolizei Schneidem�¼hl, it strains credibility that a pistol that had been transferred from there to Erfurt would have retained the same weapon number. That said, here goes!
S.S.2.II.6.23. - I believe this was the first mark applied and that it was stamped before the Schupo marking orders were issued in April 1922. It may even have been stamped before the Schupo came into existence in 1920. If so, it could be a mark for the Sicherheitspolizei (Sipo). A variety of marking schemes was in use during this time.
S.E.I.2.23. - This was the second mark applied. The first was canceled and this was stamped above it. This mark conforms to the 1922 Schupo marking order: S.E. represents the Schupo in the administrative district of Erfurt; I indicates the specific garrison in that district, probably the city of Erfurt, itself; 2 represents the particular squad; and 23 is the weapon number.
S.E.I.23. - Sometime between 1922 and the issue in February 1932 of the marking instructions in Manual 40a, the Schupo simplified their marking format. The new format included only the S. for Schupo, an abbreviation for the administrative district, a Roman numeral to represent the particular garrison (city) and the weapon number. To conform to the new rules, the second mark was canceled and this one applied to the right of the first two. It would have been easier to simply cross out the 2. in the second mark but perhaps the armorer didn't like the placement of that mark.
I hope this helps.