I am away from my references for proof marks but this sounds like a typical French shotgun made by one Mseu. F. Magand, whoever he was.
I have a similar Verney Carron shotgun that is so marked in tiny letters in with the proof marks. Verney Carron was (Still is!) a well known French gunmaker and I don't know why they did not trademark my gun more prominently.
The "70" is probably the chamber length, 2 3/4", which dates the gun well after 1897 which is just the date that set of proof marks came into use.