Assuredly an M1917 US Property pistol. As it was made in the summer of 1918, it most likely went directly to Europe as the major offensives were being implemented, and all available arms were being shipped. Mine, from the last week of Oct 1918, probably stayed stateside, and hence the very good condition.

Commercial New Service pistols were not accepted at Springfield Armory.

Many thousands of M1917 and/or M1911 sidearms were erased of their US property markings after the Great War. This is a well documented phenomenon. Nothing new here.