What indicates the start of a one-way street?

The indication of a one-way street is clearly marked by a sign that states "One Way" alongside an arrow pointing in the direction that traffic must follow. This sign is specifically designed to inform drivers that they should only travel in the direction indicated by the arrow, ensuring safety and proper flow of traffic. Such signage is crucial as it helps prevent accidents that could occur if drivers were to enter a street from the wrong direction.

In contrast, speed limit signs provide information about the maximum speed allowable but do not indicate the direction of traffic. Traffic lights control the flow of vehicles at intersections but do not specify whether a street is one-way or two-way. Pedestrian crossing signs focus on the safety of pedestrians rather than vehicle traffic direction. Thus, the "One Way" sign is the essential and clear indicator of the one-way street, making it the correct answer.