You fellows need to increase the size of your library!
O. Hi. = Ordnungpolizei of Hidesheim
The last number is the weapon number. See Don Maus' book, History Writ in Steel.
Johnny,
thanks for posting the pictures. That is a very good looking luger, very early Erfurt taken into Weimar police service. Note it has the sear safety, and the magazine safety which has been rendered inoperable. Both are key features of "police" lugers.