Which of the following signs is used for speed regulation?

The speed limit sign is specifically designed to regulate the speed at which vehicles may travel on a particular stretch of roadway. This sign indicates the maximum allowable speed to promote safety and efficiency on the roads and helps drivers make informed decisions about their speed in relation to road conditions, traffic flow, and legal requirements.

Other signs have different functions: the stop sign requires drivers to come to a full stop and yield the right-of-way; the yield sign advises drivers to reduce speed and prepare to stop but does not set a speed limit; and the one-way sign directs drivers to travel only in one specified direction. None of these signs serve the purpose of regulating speed, which underscores why the speed limit sign is identified as the correct answer for this question.