Which system component must be explicitly rated for visible or audible performance in a signaling system?

The notification appliance is the correct choice because it is explicitly designed to provide visible or audible performance in a signaling system. These appliances include devices such as horns, strobes, and speakers, which are crucial for alerting occupants about an emergency or a particular event by using sound or visual signals. This function is essential for ensuring that the intended messages are effectively communicated to all individuals in the area, especially in situations that require immediate attention.

In contrast, while the alarm panel, sensor, and control panel are all critical components of the overall system, they do not inherently provide the public alerting functionality. The alarm panel typically processes information and signals but does not produce noise or light itself. The sensor detects environmental changes but also does not provide any signaling output directly. Lastly, the control panel manages the operation of the entire system but does not generate audible or visible alerts. It is the notification appliances that are explicitly responsible for that aspect of system performance, making them a vital component in any signaling arrangement.