What does a circular road sign with a red border signify?

A circular road sign with a red border signifies prohibition of specific actions, such as no entry or speed limits. The red border universally indicates a restriction, directing drivers to take heed and comply with the rule. This visual cue is designed to be clear and attention-grabbing, making it easier for drivers to recognize rules that must be followed to ensure safety and order on the road.

For example, a "No Entry" sign will have a red circle with a white horizontal bar, clearly indicating that vehicles are not permitted to go beyond that point. Similarly, regulatory speed limit signs often feature a red border to underline the maximum speed allowed, emphasizing that exceeding it is against the law. This unmistakably conveys to drivers that specific actions are not just discouraged but prohibited, highlighting the necessity of adhering to these important regulations for safety on the road.