To me, a collar has so much more meaning than a wedding ring. Collars are not given lightly, and should not be accepted lightly either.

Most Ds only collar a cherished submissive. They take it upon themselves to take care of and love their subs. A collar is a symbol of that ownership and responsibility your D feels toward you. It's probably calming to you because you know that he would never hurt you, his cherished sub.

It's all part of getting into that sub space, and roll for the scene.