I think the use of the triskelion as a BDSM symbol can be traced back to the Story of O, where O has to wear one such ring as an advertisement of her status.

'They were strange iron rings, banded with gold inside, and the signet was wide and as massive as that of an actual signet ring, but it was convex, and for design bore a three-spoked wheel inlaid in gold, with each spoke spiraling back upon itself like the solar wheel of the Celts.'

Pauline Reage never bothered to explain why she chose this emblem, which is still widely used in Breton (Western France) jewelry.