What does a sign for overhead electric cables indicate?

The sign for overhead electric cables is specifically designed to inform drivers about the presence of power lines that are situated above the roadway. This is crucial for ensuring safety because vehicles that exceed a certain height could come into contact with these cables, resulting in severe hazards such as electrocution or damage to the vehicle. Therefore, the sign serves as a warning to alert drivers to assess their vehicle's height before proceeding through the area. It emphasizes the importance of height restrictions, making it clear that drivers of taller vehicles must take precautions or find alternate routes to avoid dangerous situations.

In this context, the other options do not accurately describe the purpose of the sign. Keeping to the left refers to traffic flow rather than height restrictions, stopping all vehicles is not relevant unless there is an immediate danger, and the presence of an upcoming pedestrian crossing does not relate to the risk of overhead electric cables. Hence, the focus on height restrictions is what makes the correct answer particularly significant for safety in driving contexts.