Many traffic lights know you’re waiting because of a loop of wire cut into the road just before the stop line. Current runs through it, and a mass of metal parked on top changes how the loop behaves: the metal sets up little currents of its own that push back. A car does this easily. A bicycle often doesn’t, and a bike with carbon wheels may barely register at all, so a cyclist can sit through cycle after cycle at a red light that has no idea anyone is there. The fix in some towns is a small painted bicycle on the tarmac showing the one spot where the wire is most likely to notice you. It’s an odd kind of sign: not telling you where you’re allowed to stand, but where you have to stand to exist.