But it doesn't meet the description given, viz. "left end of the line turned up to meet the upper line".
Yes, that's why I said "Sounds a
bit like the symbol Apple uses to represent the Option key."
Surely your imagination can devise a scenario in which the Option key symbol appears as described by Dave? Perhaps he's looking at a page on a mobil device with a small font, or a fuzzy screen cap. Point is,
I can not press that key because my Mac keyboard has no key like that! strongly suggests that the reference he encountered is a symbolic rather than literal one. I challenge you to find a more plausible speculative candidate.
