Thomas,
Greetings from the US, and thanks for the picture. No, at this point the c-S meaning is obscure. It does seem to be limited to before 1922, it does not appear to have any connection with Simson, and it has a strong correlation with back-frame numbered Lugers. Keep looking here, around the end of the month I will have an article to post about this topic which will have more details, if not an actual answer to the mystery.
In the meantime, for my research, could you please look at the first post in this discussion, and provide the information which you did not mention in your post? I will be very appreciative.
--Dwight
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