IIRC, its a tag is white with the OW logo and the word Priority on it so that they know that the back is going onward. I've seen this take on QF and CX, but almost never on AA. I take that back, on a LHR-ORD flight in J they tagged the bag, and it actually worked on arrival at ORD. Got through customs and on to my domestic flight all in about 25 minutes!