The country suffers from a bad reputation due to the number of crimes committed.
No official warnings are in place in South Africa. It's wise, however, to be on your guard as crime is at a high level.
South Africa does have problems with crime: armed assaults, car theft (often armed and at traffic lights, stop signs or in parking lots), burglaries, rapes and murders.
First golden rule is to not wear or show off valuable objects. A piece of advice that applies to pretty much anywhere in the world. Avoid certain districts in the bigger towns. Check out which are the safe places to go and take advice on which routes to use.
For example, if you're visiting Soweto, go with people who know the area or join an organised tour. At night avoid isolated, dimly lit areas and don't hang around city centres. if you're using a car, make sure it is locked day and night. Keep car windows closed.
But don't get too alarmed. By following some simple measures, you'll be fine.