D. R. P.
This abbreviation refers to a Deutsches Reichspatent, the internationally standard patents given by the newly unified German government starting in July 1877.[1]
The law defining such patents had just been passed on May 25th 1877, giving very little time to get started. There might be a strange story there.
Patent AT-1909-52940 Terms used on the patent: Filed (Angemeldet) on 31 Marz 1909 ; Priorität vom 1907; to D. R. P. Nr. 237734; Beginn der Patentdauer: 1 Dezember 1911> It's not clear why the patent term would begin in 1911 not at the time of priority or filing or grant, unless this 1911-12-01 "Beginn der Patentdauer" simply is itself the date granted. It seems that the priority reference here pertains to the filing date of this patent's earliest equivalent, internationally speaking, that is to Patent DE-1907-237734. See priority date and the protocols of the Convention de Paris pour la protection de la propriété industrielle.
