About 40 years ago, I rented a house that had a switch on the first
floor of a house, which controlled an attic light. That attic light was
always being left on. I decided to ask the landlord if I could install
a lighted switch, so it could be noticed that the attic light was on.
The attic access was a pull down folding stairs, so the attic light
could not be seen otherwise.

Anyhow, my landlord agreed as long as I furnished the switch, but
insisted that he install it. He installed the lighted switch, only to
discover that the switch box did not contain a neutral wire. And the
tiny neon bulb inside the switch needed a neutral connection. Well, he
connected that screw to the box. The box was grounded via the BX cable
going to it. The little neon bulb worked fine.

At the time I thought this was a terrible code violation, but I didn't
say anything to the landlord. 40 years later the house is still
standing. It never burned down because of that code violation. Of
course those neons draw less than one watt, so I guess it's not really
dangerous, but still a code violation none the less....