I don't believe they mean much of anything, really.
Lemme give you an example: what if you wore a shirt that said, "WWHD" & below it say "What would Hitler do?"
Hopefully, you wouldn't have a clue, lol. But that's my point. Many people that wear WWJD bracelets & T-shirts hardly know what Jesus would do because they really don't know Him. In the US, some christians would have their westerner ideas of it, & that's about it. If we don't truly know Jesus other than what He did on the cross, we're clueless of what He would do. Besides, when's the last time someone stopped you to ask about your bracelet?