Dan,
Very interesting Luger. The circle-S was stamped by and for reasons unknown, on pistols sometime between 1918-1922. There is no known Simson connection. The straight-wing eagle to the left of the proof marks may be the mark of a Heers Zeugamt where the pistol was repaired or rebuilt. It is uncharacterisic that there is no police sear safety on this Luger.
Is there a number stamped on the rear of the frame, or on the front grip strap?
I would appreciae it if you would email me about this pistol
dwightg@clear.net
--Dwight