Nice stuff Odal on the other topic!!
Well the mark indicates some sort of nickel silver. Or maybe some sort of plating over it [?]
http://www.leimat.fi/en/good-advice/nickel-silverSome info there,,but I bet theres more out there..Dates of use can probably be found and that can date your rings! [hopefully].
IF found please post here or Odals topic...thanks