What does the signal indicating 'Approach' require from the engineer?

The signal indicating 'Approach' requires the engineer to prepare to stop at the next signal. This instruction is crucial for maintaining safety on the tracks, as it alerts the engineer that the next signal may indicate the need to stop or slow down significantly. By understanding this signal, the engineer can adjust throttle and braking techniques accordingly to ensure they can respond appropriately to the next signal's indication. This preparation ensures that the train operates within safe parameters and can help prevent accidents or derailments by providing ample time to come to a halt if necessary. The 'Approach' signal acts as a warning that attention should be heightened and that the train is nearing a critical point where further actions will be needed.