I have hunted and hunted for information on “H&S O”. Any help? The initials make me think the jewelry company was founded by 2 brothers. This is an extra chucky thick sterling bracelet, most certainly from the US. It looks like a flapper bracelet from the 1920s-30s based on the open arrow back and wonderful sterling scroll work along the edges. This scroll pattern is almost identical to that found on Payco pieces (Paye & Baker).
No other information has ever come to light about the H&SO pieces, but they are from the 1920s-30s . Also, based on sales prices on eBay, they really are quite valuable. Definitely something to keep and cherish.
This may just be a starting place for identifying this mark which looks like H & S along with a hexagon to me, but Hoover and Strong make jeweler's findings, and the company has been in the precious metals business since 1912. Hoover and Strong can be searched online, and their company has contact information. Good luck if you choose to follow this route.