This is ONLY identification jewelry, also called symbol jewelry, which is worn in the BDSM scene and is an absolute identifier. The O ring, which is worn here as a necklace, is only worn by submissive women, so a man knows whether she is a dominatrix or a submissive woman or slave, and a chain is pulled through this ring on which a dom leads his sub for a walk at the BDSM parties . There is also a distinctive feature of BDSM jewelry for men. If the ring of the O, the modern one that has this ring, is worn on the left hand, it is a DOM. Why? Because the right hand is the striking hand and you don't wear jewelry on it. If the woman wears the O's ring on her right hand, that's also a sign that she's a sub, so she's submissive, because you don't wear rings on your hitting hand, and that applies to both right-handers and left-handers.
Yes, I have an idea because I myself deal with the subject of BDSM in real terms!