I just bought a yellow sapphire ring in white gold. The maker's mark is "HALLMARK" Anyone hear of that one b4?

I bought the ring online and haven't had it appraised yet. It is a rather large yellow sapphire, with 3 diamonds set in white gold. It is a pear cut sapphire and set in the ring to look like an unopened rosebud. The leaves that run along the bottom are etched. I can not find anything on the "HALLMARK" maker's mark, becuase just the word "Hallmark" brings up too many responses. Any help would be great!