What type of sign warns you of the highest safe speed for a turn ahead?

A diamond-shaped warning sign is designed specifically to alert drivers to potential hazards or changes in road conditions ahead, which includes warnings about turns. When you see a diamond-shaped sign displaying a recommended speed for a turn, it indicates the maximum speed a driver should maintain while navigating that turn safely. This type of sign is crucial because it helps ensure road safety by informing drivers of the appropriate speed to reduce the risk of losing control in a curve or turn.

The other sign shapes serve different purposes; rectangular regulatory signs typically communicate specific laws or regulations that must be followed, circular guide signs provide important navigational information, and square informational signs convey various types of information, but none of these serve the warning function related to safe turning speeds like the diamond-shaped warning sign does.