Which of the following is not a type of sign classification?

The classification of signs is typically organized into several categories based on their function and purpose on the road. Regulatory signs are established to inform drivers of laws and regulations they must follow, such as speed limits or parking restrictions. Warning signs alert drivers to potential hazards or changes in roadway conditions, such as curves or pedestrian crossings. Guide signs provide useful information related to routes, services, and points of interest.

While railroad signs do exist, they do not constitute a separate classification broadly recognized in the same manner as the others. Railroad signs are a specific type of warning sign, specifically designed to alert drivers and pedestrians of railroad crossings. Therefore, they do not represent an independent category within the standard signage classifications used in traffic regulation. This framework helps keep roadways safer by ensuring that drivers can quickly and easily comprehend the signs they encounter.