can someone tell me what do the letter inside trapezoid mean. I found this mark on old necklace. I suppose its only american double, but the stones are very interesting (similar color to tanzanite).
It is a probably the maker's mark, indicating who or what company made the piece. There are many books and several sites which list maker's marks if you want to look it up but, if the maker is small and unknown, it may not be listed.