My current surge protector has three lights on it: a light labelled "Surge," a light labeled "Ground," and a light on the switch itself.
The ground light can only report on safety ground. Surge protection is about earth ground. Nothing can detect earth ground from a wall receptacle. If the protector manufacturer does not discuss that, then many will assume all grounds are same.
The light can only report a safety ground failure. It cannot even report the safety ground is good or sufficient.
Light on the switch is a power light. Same device also found in lighted wall switches. As a neon bulb ages (as the neon gas inside becomes contaminated), that bulb flickers.
What does the third light report? Well, the light can report a type of failure that must never happen. If that failure occurs, the protector was grossly undersized. Should not have been purchased. If the MOVs had not disconnected fast enough, then a potential house fire existed. Effective protection means grossly undersized protectors should never exist. But a grossly undersized protector gets the most naive to recommend that protector. Grossly undersizing means many will recommend that protector.
And finally, a picture of all MOVs removed from a protector. The light still says the protector is good. Of course. That light only reports one type of failure. Cannot report any protector as good:
http://www.zerosurge.com/HTML/movs.html
Effective protection costs abut $1 per appliance. Nothing adjacent to the appliance will accomplish effective protection. But as demonstrated by those lights, many will make recommendations without first learning the underlying science.
Even that ground light does not say anything about surge protection. It can report a bad safety ground. But cannot report a good safety ground.