The earliest Lugers--Old Model 1900 series--were marked on the right side rounded end. Somewhere between Luger #7094 and #7108 the number moved to the left face for a brief time. Somewhere between #7735 and #7857 the number moved to the bottom, proper for Commercial (hidden-number) style Lugers, where it remained for Commercial guns.
If DocLes's Police Luger has commercial proofs (crown/N) the position is proper. A large percentage of Weimar-era Police Lugers came from DWM commercial production, so this is to be expected.
The Army Instructions for marking P-08, mandating exposed (military style) markings, were issued in 1910. DWM Army Lugers made before this time will have the takedown lever numbered on the bottom, after this date they will be on the exposed face. Luke's survey is primary data here.
As Erfurt was exclusively an Army armory and didn't produce Lugers until 1911, all Erfurt takedown levers will be marked on the face.
Imperial Navy Lugers were not subject to the Army's marking instructions, and so these will have their takedown levers marked on the bottom.
Simson Lugers which were manufactured as part of their Weimar Army contract should be expected to have their takedown levers stamped on the face, as the marking instructions appeared to stay in force throughout the Luger's lifetime. Photographs in the literature seem to bear this out, although I have not seen any documentation to support this. Simson reworks are a mixed bag.
Krieghoff, being a Luftwaffe contractor, was also not bound by the Army's marking system. According to Gibson, Krieghoff military guns below #2500 were numbered on the face of the takedown, after that number were numbered on the -inner- surface of the flat.
Contract Lugers will be numbered variously depending on their origin.
Other correspondents will have to respond regarding Mauser Commercial Lugers and Swiss Lugers.
--Dwight