Signs of this kind are funny because they collapse two different jobs into one line. A real electrical warning has to say what the hazard is, who may work on it and what to do first — isolate, lock off, prove dead. A sign that only says not to touch anything conveys alarm without instruction, which is precisely why it reads as a joke to anyone who has done the work.

The practical version is duller and better. Labels identify the circuit and its voltage, a lock-out device physically prevents re-energising, and the tag carries the name of the person who applied it. Where photographs like this one are worth keeping is as a reminder that a warning nobody can act on is decoration. The picture is held here as an archive entry.