Looplok

The looplok (sometimes spelled looplock or looploc) is a lock worn fastened to a beltloop to discreetly signify that the wearer is locked in a chastity device. A looplok may be worn to signify a person's commitment to chastity or as a vanilla friendly way to be recognized by other people in the lifestyle.

This is a similar signal to the way a keyholder may wear key jewelry.