For safety reasons, you carry two reflective triangles and an OK / + board in the car. The triangles go out up the road to warn following cars that there's a buggered car ahead, and the OK is to say just that. On the other side of the OK board, there is a black cross on a red background (see previous pics of my car), which means "help". If you see that, it means that someone is hurt, and you stop and give assistance. The car behind then also stops, takes details and goes to the next radio point to get help. :D
The system works! :)