There is a listing in the Hougart book for MS that says: Stylized, Taxco Mexico 940 Eagle 3. No name with it.
It sounds like your mark but I don't know about the eagle 9 mark, there are 8 names listed with it but none that are MS or even S.
It's more common to not be able to ID a Mex designer.
(admin edit - see Posting Requirements)