Needed: An international hand signal for "There's a problem with your car"
You're driving down the road. You see another car on the road with you that has a problem. The lights are off and it's dusk. There is something loose that may break off. There's something left on the roof or the trunk is not closed -- any number of things. How do you tell the driver that they need to stop and check? I've tried sometimes and they mostly think you are some sort of crazy, driving to close to them, waving at them, honking or shouting. Perhaps after a few people do it they figure it out.
We have a few signals. Oncoming cars flash lights on and off to warn you your lights are off. (Sometimes they are also warning of a speed trap.) High beams means, "I want to pass and you're impeding the lane" and while many think that's rude it's better than tailgating.
We need a signal for "There is a problem with your car, you should check it out." This signal should be taught in driving schools, and even be on the driving test. A publicity campaign should educate existing drivers.
One proposal that might make sense is the SCUBA signal for "I have a problem." This is holding your hand flat, palm down, and wiggling it side to side (ie. rotating your wrist.) Then you point to the source of the problem, like your regulator or whatever. (There are specific SCUBA signals for well known problems, like being low on air, nitrogen narcosis etc.)
For this signal you would waggle the hand and then point at the place on the other person's car. To those untrained, the signal often mean's "dicey" or uncertain. Shaking of the head could also strengthen the signal.
Anybody have a better signal to propose?