What type of sign warns you that you must slow down?

The correct choice is that yellow diamond warning signs are designed to alert drivers to potential hazards and the need to slow down. These signs convey important information about upcoming changes in road conditions or obstacles that may require a reduction in speed for safe navigation. Common examples of situations indicated by yellow diamond signs include curves, intersections, pedestrian crossings, and construction areas, all of which often necessitate a decrease in speed to maintain safety for both drivers and pedestrians.

Red stop signs are specifically used to instruct drivers to come to a complete stop, while rectangular regulatory signs generally provide instructions or information necessary for proper compliance with traffic laws. Green information signs offer guidance on directions, distances, and locations, but they do not indicate any requirements to adjust speed. Therefore, yellow diamond warning signs are uniquely suited for the purpose of warning drivers to slow down.