Purpose of a "mystery key" on an IBM PC 3270 keyboard

I do know the symbol on the bottom right key as being the symbol typically used when proofreading written documents. It is a delete. When you write that over a letter or word in a paper, it indicates that it is unneeded and should be removed. Seeing as how this is an older keyboard, the users of the equipment at the time likely would be very familiar with proofreading symbols and understand what it represents.

My guess (without having used the machine in question) is that it likely is the delete key.

This page goes through a history of some IBM keyboard layouts, and a few pages down you see this image:

You can see the key layout in your screenshot above the arrow keys. The key layout is:

Dup/PA1    FM/PA2    PA3

Back Tab   Insert    Delete

The delete mark on the key makes sense, especially combined with the proof-reading mark also used for "insert".

This is an IBM 6110344 keyboard and the keys on the 6110344 are laid out like this:

So the key you're looking for corresponds to scan code "6D". When we look at the related scan codes on the link given above, that key turns out to be Del, namely Delete.

The symbol you nick named as 'person in wheelchair being chased down a hill by a boulder' is for indicating that the alphabet is wrong.

Closely looking at the key we can separate the a and the other symbol .

The other symbol is indicating wrong sign.

something like we use for right & wrong . This symbol is shown in slightly different angle indicating strike off the alphabet (or delete the alphabet).

(a/°) is the DEL key. At its left is the INSERT key (â).