What can be a visible sign of a faulty surge protector?

A visible sign of a faulty surge protector is burn marks or discoloration. When a surge protector experiences excessive electrical surges or failures, it can overheat or be damaged internally. This overheating can cause burn marks on the exterior casing, which serve as clear indicators that the surge protector has been compromised. Discoloration can also indicate that the materials used in the surge protector are melting or degrading due to excessive heat, further confirming that it may no longer provide effective protection against power surges.

The other options do not indicate faultiness. A smooth exterior finish is typical for many surge protectors and does not imply any issues. Flashing lights indicating working status typically suggest that the surge protector is operational and functioning correctly. Excessive weight could be a characteristic of a heavy-duty surge protector but does not inherently signify that it is faulty. Therefore, burn marks or discoloration is the most accurate sign of a surge protector that is no longer safe to use.