On P.38's, that type of mark is usually for a part that had to be re-worked in the factory.
That was a mark that Walther used for parts that were first rejected and then reworked before they were used on an accepted gun.
Seems to be the accepted. Answer for these markings.
Do I also seem to recall the mark was in the out of spec area to be reworked?
..My guess on this particular example is that the diameter of the barrel was off so it had to be machined for the front sight sleeve to fit. Sometimes you see an extra inspection after it was fixed. We see this a lot with Spreewerk slides in particular.