When should a yellow tag be applied to a system?

Applying a yellow tag to a fire alarm system serves as an important indicator of compliance with safety standards and regulatory requirements. The correct answer emphasizes that a yellow tag is warranted after any service, inspection, or test reveals that the system does not comply with applicable codes. This protocol is crucial because it alerts users and inspectors that the system is not fully operational or may pose a safety risk, thus fulfilling a key role in maintaining fire safety and ensuring that any issues are addressed promptly.

In cases where a system fails to meet compliance, the yellow tag serves as a warning that the device should not be relied upon until it is brought back into compliance. This practice is integral to the maintenance of safety standards within the fire protection industry. By identifying noncompliance in a clear and recognizable manner, it prevents potential misuse of the system while remediation occurs.

In contrast, the other options relate to different scenarios where a yellow tag is not typically required. For instance, merely being six months post-installation or showing normal functionality would not necessitate a yellow tag. It's the failure to meet the necessary codes and regulations that triggers the need for such tagging.