In California, I've seen single-socket traffic lights in all three colors. So it wouldn't have to be custom-made. The green ones usually have a directional arro

In California, I've seen single-socket traffic lights in all three colors. So it wouldn't have to be custom-made. The green ones usually have a directional arrow forward (amber and red usually blink) so they could probably accomplish the same effect with stock parts: red arrow pointing right in a single socket.