Peppersgirl, I don't think there is any hope for horses not crossing the border branded or not. I think a deterrent only because the horse will be more readily identifiable.
I honestly don't think that the auctions are looking at the horse and/or paper work in a way looking for a stolen horse. Just looking at it to make sure it is in the shape it needs to be included in the sale. I bet they never look at a brand to match up paperwork if it is being run in loose. Just let the whole truck load in :(