What type of sign indicates a mandatory action?

A circular sign with a blue background indicates a mandatory action. This type of sign is designed to communicate to drivers that they must follow the directive presented on the sign, such as "Turn Left" or "Keep Right." The blue color is specifically used to signify something that is obligatory, differentiating it from danger or warning signs, which use other shapes and colors, such as triangular warnings or rectangular information signs. This standardized use of colors and shapes helps create clarity and consistency on the road, ensuring that drivers can recognize and comprehend the rules they are required to follow.