Exciting mystery

I’ve managed to buy an old sterling silver necklace for just under £30 with very worn silver marks. It looks kind of 1930s to me and almost pewter-like so needs a good clean.

The silversmith mark is OJ (I think) and there is an unknown silver mark on it, aside from a ‘925’ for silver and a very worn date letter. The nearest thing I can find to the unknown silver mark is something called a ‘Leo mark’ used on watches back in the early 1910s, possibly to indicate imported silver. I’m thinking it may be a Danish piece but beyond that I’m stumped!

I will be cleaning it as I intend to wear it regularly :-) I’m partly blipping this in case I wear the remaining silver marks off and the information is lost forever.