Every day thousands of hands stretch out along commuter routes across Gauteng, communicating silently with the drivers of minibus taxis. A raised index finger indicates you are headed to the city centre; turn your hand palm upwards and curl your fingers around an invisible fruit, and your destination changes to the informal settlement of Orange Farm.

This ingenious system was developed during the apartheid era by black commuters, who had to travel long distances to and from work without easy access to transport.

Johannesburg artist Susan Woolf has documented what is arguably South Africa’s 12th official language in her books and exhibition, Taxi Hand Signs: Symbolic Landscapes of Public Culture.

The easiest way to test the system is to ride a minibus taxi to the city centre, and the best way to understand it without the handbook is to ask other commuters.