Purpose of a 'mystery key' on IBM PC 3270 keyboard

This remains the standard mark for deletion in today's publishing industry. Yes, we still often edit books in three to five inch stacks of paper.

People have actually paid me to do editing (the fools!), and I know the standard proofreading marks backwards and forwards, but I still didn't read the graphic on the key as "delete". I might have been able to suss it out if you told me it was supposed to represent an editing mark but looking at it absolutely cold? No way.

The person who designed the keycap probably had to cobble it together from a set of standard characters/symbols. If they'd used a more freehand representation, like the one shown on the 6110344 layout further down the page, it would have been immediately obvious.

I'm only 22 and was taught the same marks in elementary school. I wouldn't have recognized it on the key right away, but once it was mentioned, it made sense.

Not taught in UK education (private, I assume not in state schools either) as of at least a decade ago, I only know them because my mother is an author.

In the US? I'm a few years older than you, and I'd never heard of such a thing - we went straight to word processing on Apple ][s.

Not here in Germany (although the German standard DIN 16511 seems to come pretty close to the US ISO 5776).

I'm 34 and learned them, wouldn't surprise me if they're not taught now.

Not in my school.