Circle S mark on Luger Receivers

I have asked this question previously without response. Jan Still pictures Lugers with this mark and says "meaning unknown" Costanzo says Simson rework. With recent blast of Costanzos work on forum---Did he invent this to authenticate some Luger or does Still just not know? What do you think? Any other theory? Iam interested in comments based on some research to dispute Simson theory. Not just spectulation and wild guesses. I have Lugers with this mark. Does anyone else? I am still awaiting something to confirm that Costanzo's World of Proof Marks has a bunch of invented info and inaccurate information? Or was the recent put down of his book just a put down to the man? One responder promised to post inaccuracies in Constanzo's book and another contacted me directly who was concerned about liability, but would send info directly. As yet no info has surfaced to me to dispute Constanzo's World of Lugers proof mark book. If inaccuracies exist in the book; I suggest that those who have documented info and research to dispute parts of the info come forward in a respectful manner with back up research and let the Luger world know the latest.