Hello Heinz,
The L.Z.A. was a collecting point for hides. The hides were checked and after acceptance they got the typical marking:
-L.Z.A.
-Prussian eagle
-town, where the facility was located.
After this procedure the hide could be delivered to the commercial manufacturers. The L.Z.A. had therefore two tasks: quality control and a local quantity control.
The mentioned marking is often to be found somewhere on the holster, because the marked section of the hide was not selected and used as it was.
Look to the image of kidvett or in the book "J.P.Sauer & Sohn, Vol. II" by Jim Cate and Mrtin Krause on page 62. In both cases the mentioned stamp could be found on an indefinable place, partly cut away or oversewn.
If it would be a quality inspection mark for a finished holster, you can be sure that the German army would have instructed this procedure and the stamp would have always the same place and design.
regards