All numbers on all pieces of the gun match, a small "m" looking symbol is seen under the barrel and around the trigger. (mauser?)
The small M could be part of the SN. A crown/M stamp was a WWI era Navy marking.
"M" would not be for Mauser. If the gun is a DWM, it cannot also be a Mauser. Its kind of like saying you have a Ford Chevy truck - either one, or the other. DWMs are marked with scrollwork on the rear toggle, and Mausers are marked either S/42, 42, or BYF on the top of rear toggle. The Mauser codes were "secret" since production of 9mm lugers violated the treaty of versailles before WWII and then they were kept secret code so the allies could not prove where the arms were being manufactured IE which factory to bomb.