What is an indicator that confirms the operating state of signals in a tower?

The "signal can clear light" serves a crucial role in confirming the operating state of signals in a tower. This indicator provides visual confirmation that a signal is clear and that train movements can proceed. When the light is illuminated, it indicates that the signal is in a state that allows for safe passage, ensuring operators can make informed decisions regarding train movements based on the actual state of the signaling system.

Other options might provide information or context related to the operation of the signal levers or the system, but they do not offer the direct confirmation that the "signal can clear light" does. Lever color coding might help in identifying signals based on their status, but it does not directly indicate clearance. Similarly, lever stop parts and call on buttons serve different functions within the tower operations but do not confirm the operational state of signals in the same clear and direct manner as the light does.