Which characteristic is true for warnings signs?

Warning signs are designed to alert drivers about potential hazards or changes in road conditions. This characteristic is crucial for maintaining safety on the road, as these signs provide important information about dangers that may not be immediately visible, such as sharp turns, pedestrian crossings, or road work. The goal of warning signs is to prepare drivers for what lies ahead, allowing them to take appropriate action to reduce speed or navigate safely.

In contrast, the other options do not accurately represent the characteristics of warning signs. For instance, warning signs are typically diamond-shaped and not square or octagonal, and they do not have green lettering, which is usually reserved for informational signs. Thus, the understanding that warning signs primarily indicate hazards is key to recognizing their role in road safety.