What indicates that you are approaching a sharp curve?

The presence of a curve speed limit sign is a clear indicator that drivers are approaching a sharp curve in the road. This type of sign is specifically designed to alert drivers to reduce their speed in anticipation of a change in the road's direction, which is crucial for maintaining safety and control while navigating through the curve.

In contrast, the other signs listed serve different purposes: a pedestrian crossing sign informs drivers of areas where pedestrians may be present, a straight road sign indicates that the road ahead continues straight without any turns, and a one-way street sign indicates the direction in which traffic is permitted to flow. None of these other signs provide information about upcoming curves, making the curve speed limit sign the correct choice for this question.