Yeah, apparently a bell given to you is the way they work. After that if it falls off or something it's okay to buy your own replacement.
I heard they got started way back when a cart pusher (and just to clarify, that would be somebody pushing a cart) might have a bell on there somewhere. Then, while attending a pub for a wee nip, or sleeping off a few wee nips, the bell wound alert the owner that someone was messing with his cart.
