Bikes are small critters and often don't trigger the traffic light sensors at intersections leaving the poor cyclist facing a red light with no traffic in the intersection. To get around this, many major intersections provide a button for the cyclist to hit, just like the button used to activate the pedestrian crossing - it even has a cute little push bike symbol on it.
A lot of pedestrian crossings have been set up to help the blind - that button makes different noises depending on what part of the cycle it's in.
I pulled up at an intersection recently, and the 'cyclist' button, complete with dinky little push bike symbol, was one of the noisy 'blind' buttons.
Mind you, the way some people ride their bikes, you could be forgiven for imagining that many cyclists are blind.