Just taking a guess but maybe a later refinish. The lettering below the unit mark looks to be blued over some pitting. I can’t tell if it is the pictures but the finish looks dull almost has a parkerized finish.
Jim
A community dedicated to Lugers, Central Powers, Axis, Allied and related WW-I and WW-II pistols by their scholars, collectors, owners and enthusiasts. Come join the discussion about the history, technology and extraordinary background associated with these design masterpieces.