Collars are an indication that a particular Pretty Boy belongs to a 'Cut'.
He may get mocked for taking an easy route and giving up on getting his name back by the others.
However it is a sign he should not be touched for a fight unless you are trying deliberately to pick an argument with his 'Owner', who will come after you.
It is considered bad taste and weak to send a challenge this way.
Collared Pretty Boys can be used any way their owner sees fit.