Bruce, it is very rare to find a Luger that had a sear safety removed during its service life. I have observed only two situations in which this might be the case. In some instances, a police Luger apparently was transferred to the German military and the safety was removed. This post is one example:
http://forum.lugerforum.com/showthread.php?t=23910. Police Lugers captured by the Russians also had their sear safeties removed.
I don't think your gun was transferred to the military. No other Luger with this marking has had its sear safety removed. I would expect that the whole unit or a significant part of its inventory would have been transferred.
I see no sign that this gun was captured by the Russians. There is evidence presented in HWIS to support the idea that these Lugers were captured in Bavaria by US troops.
While almost anything is possible, I think it likely that the sear safety was removed and the side plate replaced some time after WWII. This also raises the possibility that the notches were filed at a later date.