I keep seeing this symbol on old electronics appliances of varying types.
Two examples that I own…
Early 1960's portable "Megger" insulation tester
July 1969 Marconi attenuator
I have also seen this on other equipment manufactured as late as the 1980's, such as an HP 3314A signal generator.
So, it appears that this is a standard symbol, and not a proprietary one.
What does it mean?
Final edit to add another photo as supporting evidence for @Spehro Pefhany's answer
Best Answer
The Broad Arrow (aka 'pheon') indicates that the item in question was once (British) Government property - a Crown asset.