A lot of people ignore them, and just cross according to the road vehicle lights. I arrived at a cross-ride a couple days ago with a bicycle beg button for the cycle light. There were some cyclists already there when I got there so I assumed they hit the button until the car traffic went green and the bike signal stayed red. They rode across and I advanced to hit the button, immediately making the bike signal green. I have to wonder what the point of it all is.