An example of a regulatory sign is: Mile Marker Signal Ahead Do Not Enter Road Construction Ahead

A regulatory sign is a type of traffic sign that is used to inform drivers and pedestrians about the laws and regulations that apply on the road. These signs are typically rectangular in shape and have a white background with black or red text and symbols. They are designed to convey specific instructions or warnings to road users. Among the options provided:<br />1. "Mile Marker" is not a regulatory sign; it is an informational sign that indicates the distance from a specific point, usually a city or landmark.<br />2. "Signal Ahead" is also an informational sign; it warns drivers of an upcoming traffic signal or intersection.<br />3. "Do Not Enter" is a regulatory sign. It is used to indicate that a particular road or area is not open to vehicles, and drivers should not enter.<br />4. "Road Construction Ahead" is an warning sign, not a regulatory sign. It warns drivers of upcoming road construction or maintenance work.<br />Therefore, the correct answer is "Do Not Enter" as it is an example of a regulatory sign.