A white circular sign with a red circle and slash over a symbol means:

A red circle with a diagonal slash through it placed over a symbol is the standard 'prohibition' marking — it means the action shown is not allowed. For example, a left-turn arrow inside a red circle and slash means 'No left turn,' and a U-turn arrow with the circle and slash means 'No U-turn.' These are regulatory signs stating rules drivers must obey. The red-circle-and-slash is an internationally recognized symbol for 'do not.' Recognizing that this marking prohibits the depicted action — rather than permitting or warning about it — is important regulatory-sign knowledge for the permit test.