Which of the following is a warning sign?

The term "Caution" refers to a warning sign on the road, typically signaling drivers to be aware of potential hazards or changes in road conditions. Warning signs are designed to alert motorists to specific dangers that may not be immediately apparent. These signs can indicate a variety of situations, such as sharp turns, pedestrian crossings, or road work ahead. The use of "Caution" emphasizes the need for drivers to reduce speed and remain vigilant.

In contrast, the other options represent different types of roadway signage. "Yield" is a regulatory sign that instructs drivers to give way to oncoming traffic. "Do Not Enter" is also a regulatory sign that directs drivers not to enter a specific area, typically a one-way street going the wrong way. "Exit" typically indicates a freeway or highway exit, giving directions to leave the highway, and is also not considered a warning sign. Each of these has distinct purposes that differ significantly from the role of a warning sign.