The general prohibition sign, [1] also known informally as the no symbol, ' do not' sign, circle-backslash symbol, nay, interdictory circle, prohibited symbol, don't do it symbol, or universal no, is a red circle with a 45-degree diagonal line inside the circle from upper-left to lower-right.

Prohibition signs specify behaviour or actions which are not permitted. The annulus and slash should be depicted in red over the action symbol in black. Prohibition Sign wording, if necessary, is in black lettering on a white background.

Prohibition signs are a type of sign used to try and prevent various activities in certain situations. They’re commonly used to identify actions that are either not authorised because they do not conform to the rules and regulations of a given area, or that those actions could potentially cause a risk to the health and safety of bystanders.