Travellers coming to South Africa probably all wonder about the hand signals people along the streets and roads use to stop minibuses. All these hand signals do indeed have a special meaning and indicate the person's next destination, or the taxi route they would like to follow.
The system is pretty complex and you need to have a very good knowledge of the area to fully understand it. Therefore the City of Johannesburg created a Taxi Hand Signals User Guide (pdf) to give an overview and to make the system somehow understandable. Well, good luck!