This mark is found on Simson marked Gew.98 rifles, but not exclusively. Neither Simson nor any other of the Suhl gunmaker involved, Sauer, Haenel or Schilling, made a single receiver! The special machines simply were not available in Suhl. All Suhl gunmakers had to use machined receivers supplied by the state arsenals Spandau, Erfurt and Danzig. Receivers were also supplied to them by Siemens & Halske, Berlin, and H.Pieper, Liege, Belgium. (I suspect Pieper was merely a straw man for FN. Officially FN did not collaborate with the occupying Germans, but the stock majority of FN was held by German DWM and Pieper pre-WW1) The government arsenal Spandau alone had to make 1000 receivers per day to supply the Suhl guntrade. All the Suhl gunmakers subcontracted parts making and swapped parts. So most of the Suhl guntrade was involved in making Gew.98 rifles. Read Dr. Dieter Storz’ book “Rifle & Carbine 98. M 98 Firearms of the German Army 1898 to 1918.” (about 460 pages) Storz, of the Bavarian Army Museum, is the foremost historian of military arms and production up to WW1.