You didn't mention the caliber stamping, but with a 5" barrel, at this serial from mid-1943 it can only be a Lend-Lease British Service model in .38 S&W. If it's actually "parkerized", it's a refinish, but you're most likely talking about the original sandblast black magic.

No S to be expected unless parts failed final inspection, and during that time the P was no longer applied consistently to the butt, and was not yet used in its new three locations.