Can anyone tell me what this marking means. While familiar or able to locate many jewelry markings this is new to me and am thinking about purchasing. All I know is that this a vintage piece, I suspect the 60s , but really not sure and it is about 1 1/18 wide and 7.5 inches long with safety clasp and insert closure. On the inside closure there is a marking which reads "CT18750". Any information available would be appreciated. Thank you.