That’s a conjoined ‘S’ and ‘b’, which is the mark for Shube’s Manufacturing Inc. of Albuquerque, NM. They started making jewellery sometime in the 1960s, operating as a wholesaler and mail order business. In 2006 they were acquired by an Ohio conglomerate and continued trading under the new name “Shube’s Inc.” until late 2008 when they merged with the South Dakota Gold Company and then operated as “Dakota West Design” within the Ohio conglomerate.