What do I have here?

[Lugerdoc]

John F, Your suffix letter is definately an R. The partial eagle stamp under the barrel, looks a bit like a Simson Weimar era rework stamp. I think rather than a Police marking, the "P.K.xx" on your grip strap, translates to "Personen-Kraftwagenpark des XX armeekorps" or the Passenger Vehicle Depot of the xx Army Corp. (see Jeff Noll's "Imperial German Regimental markings" page 40. Tom H.