What type of sign warns drivers of upcoming curves?

The correct answer is a yellow advisory sign with a curve symbol because these signs are specifically designed to alert drivers to changes in the road ahead. The yellow color and curved symbol indicate the nature of the upcoming road condition, allowing drivers to prepare for a turn or bend in the road. By providing this essential warning, the sign helps ensure that drivers can adjust their speed and steering appropriately, enhancing safety and reducing the likelihood of accidents.

Other types of signs serve different purposes: a stop sign indicates a need to halt and yield to other traffic; a green directional sign provides information about routes and destinations; and a blue informational sign typically conveys services or amenities nearby but does not alert drivers to changes in road conditions. Each sign plays its own important role, but the yellow advisory sign with a curve symbol is the one specifically aimed at warning about upcoming curves.