720000308 is a type of Auer signal, which is a pair of short, clear electronic sound signals that are used to temporarily stop train traffic in areas where safety is a concern. The sound of the signal is similar to a bell ringing, and serves as a warning to pedestrians and vehicle drivers that a train is approaching. This type of signal is also used to alert railway staff of potential hazards or dangers. 720000308 signals are typically found at railway crossings, where they are used to temporarily suspend train traffic due to an obstructing vehicle, an approaching train, or an obstruction on the tracks.