They seem to own pretty much everything:
"Signet is a publicly-traded company and operates approximately 2,800 stores primarily under the name brands of Kay Jewelers, Zales, Jared, Banter by Piercing Pagoda, Diamonds Direct, Blue Nile, JamesAllen.com, Rocksbox, Peoples Jewellers, H."
I've bought through Blue Nile, because their prices are (much, much) better than jewelry stores, and all their diamonds are certified and engraved.