Which of the following indicates a stop sign?

The red octagonal sign is universally recognized as a stop sign. Its distinct shape and color are specifically designed to attract attention and signify that a driver must come to a complete stop at an intersection or where the sign indicates. This shape and color combination is standardized in traffic regulations to ensure consistency and enhance safety, allowing drivers to recognize the sign quickly, even from a distance.

The other options represent different types of signs: the yellow triangular sign typically indicates yield or caution, the blue circular sign is often used for guide signs indicating amenities or services, and the green rectangular sign usually provides directional information or guides. The specific characteristics of the stop sign—its red color and octagonal shape—are crucial for ensuring that drivers respond properly at critical road junctions.