What defines a railroad sign or signal?

A railroad sign or signal is specifically designed to inform drivers and pedestrians about the presence of railroad tracks and the possible approach of trains. This serves an essential safety function by alerting those near the tracks to be cautious and aware of potential dangers. Understanding and recognizing these signals is critical for preventing accidents at railroad crossings, where there can be a high risk due to the speed and mass of trains.

In contrast, the other options do not pertain to railroad signals. For instance, a signal indicating a vehicle's speed limit is related to general road traffic regulations, while warnings for road construction address temporary hazards unrelated to trains. Additionally, a streetlight for pedestrian traffic serves a different purpose, focusing on guiding pedestrians rather than alerting them to railroad hazards. Therefore, the fundamental role of a railroad sign or signal is to provide clear and specific indications regarding railroad safety.