You might have perhaps seen my picture of Molly? If so I don't want you thinking it was because it looks cool, I would never leave a collar on a rabbit for a long time, they could severely injure themselves.
He wore it for a little while when I came back to my parents because of the jingly bell on it. The layout of my parents place makes it hard to block off certain places so whilst he was getting used to the new environment, and we were learning where he could get in to trouble (such as behind a very heavy tv stand with lots of dangerous wires stored behind it one time
) it was useful for us to be able to hear where he was. It was a cat safety collar and he never wore it without people around and no longer needs it. I only got one under the reccommendation of a friend from the US, who at the time was the only person I'd ever met who'd had house bunnies.
But I'll admit, it does make a cute picture.