What indicates an Approach Signal's identity in an interlocking system?

An Approach Signal's identity in an interlocking system is indicated by a white plate featuring a black "X." This is standardized in rail operations to inform operators of the specific nature of the signal they are approaching. The black "X" serves as a clear and recognizable marker, ensuring that train crews can identify the signal's purpose quickly, enhancing safety and operational efficiency as trains prepare to enter a more complex or potentially restrictive track area.

In rail systems, signaling is crucial for safe train movements, and specific signals are designed to convey particular instructions or warnings to the operators. The use of a white plate with a black "X" is an established and uniform practice that avoids confusion with other signaling components that might use colors or lights for different meanings.

Other signal choices presented, like red lights or green lights, typically denote restrictions or clearances, not the identity of an Approach Signal. Thus, focusing on the distinctive marking of a white plate with a black "X" accurately represents the specified signaling identity within the interlocking frameworks of rail systems.