MIke;
My first thoughts are that it might be an old Siemens steel trade mark but I have not been able to find it on the internet searches. I had a 1888 British gun in the past that had Siemens steel barrels, but it was stamped with "Siemens steel" not a trade mark. However that does not mean that that the subject trade mark is not that of Siemens. If I find anything I will post it to you.
I saw where Cal Pappas near you in Willow, Alaska died of a heart attach a couple of weeks ago while he was packing his bags to return to Africa for another hunting trip. It was terrible new to hear that he had died. I suspect that you and Cal were friends. I have communicated with Cal through the years via email and in the years past about double rifles, but we never met.
Stephen Howell