This is a wartime Walther PP holster with a leading edge magazine pouch instead of the standard holster having the spare magazine pouch placed on the front of the holster. This style of proprietary holster was manufactured by holster maker Albrecht Kind (Akah) during and after the war. There is a famous black/white period postcard of two Sicherheitspolizei (SIPO) officers wearing this style of holster while on active service in the East. Clearly, this style of holster was utilized by SIPO and SD Officers but it was also available for private purchase from Albrecht Kind as it was listed for sale in their circa 1938 catalog.
This black leather holster has the wartime Akah logo with "D.R.G.M." above it. Postwar KInd made holsters do not have the DRGM patent marking. This holster is first found in the circa 1938 Akah catalog which makes it a bit late for being an item of issue with the first Walther PP and PPK that are identified by serial numbers as being issued to the SIPO and SD. It appears that these SIPO/SD pistols made before 1938 were issued with black leather Theuermann patent drop holsters. Arved Theuermann was an SS Officer who served in the Waffen-SS and designed, and patented, his drop holster which the SS bought and issued. But that is a different holster and another story.
These leading edge magazine holsters (not the drop holsters) are quite scarce and those made in black leather are doubly so.