The bikes used to have bells, but then it was way too easy to get your wings.
This is my idea for the New Yorker Cartoon Caption Contest #316. In case you don't get it, it is a reference to the movie, It's A Wonderful Life, where Zuzu says, "Teacher says every time a bell rings, an angel gets his wings." You see, if the angels had bikes with bells on them, they could just ring them and get their own wings. Obviously, it isn't funny if you have to explain. Let me know if you have any ideas for a caption too.
