Had one on my bag on my recent San Francisco trip. Dont know if it made a difference on the way there as it took that long to get through immigration that all the bags were piled on the floor next to the conveyor belt. However on my return from Heathrow from plane to baggage claim was just shy of ten minutes, and my bag was already waiting for me on the belt with other bags with the yellow tags.

I have a picture of one I'll try to post for JMurray

Bri