nev
Super Térrarist
I noticed in Indonesia (where you drive on the left) that if you are in a queue of traffic trying to overtake, the cars in front will indicate left meaning "safe to overtake me". Indicating right means "don't overtake, oncoming traffic".
In india, a sharp toot of the horn advises a truck driver that you're going to overtake him, then you keep a keen eye out on his driver side window and he will stick his hand out either waving it subtly forwards, advising that it is safe to overtake, or waving it downwards, indicating not safe to overtake. After the overtake manouevre you give 2 toots of the horn to say thanks.