Railway signal
On older lines semaphore signals are still used.  These are poles with a coloured bar at the top, which can be moved so that it is either horizontal, or at an angle.  When a red bar is horizontal this means that the train must stop, and when it is pointing diagonally up or down it means that it's safe for the driver to continue.  There are also signals with yellow bars which give warnings in the same way as yellow lights on newer signals.