My first answer is that it is a "check protector" type of character, designed to be typed over the amount on a check* to prevent or at least make it very difficult to erase the amount and type in a different value. Of course it can be typed over anything else you might want to protect from alteration. Type your amount, then backspace and type this character; you can still read the value easily.

It could conceivably be a logic character, like "therefore" or "exclusive or" but I really doubt it here.

It's not a margin release, nor tab, etc., because it's on a key that actually types a character. Typewriters don't have keys that mix functions like that.

* A check was a small form, the size of a dollar bill, that operated like an IOU, in that you would fill in the amount to be paid, to whom, and give it to the person that you were paying, who would then give it to their bank and their bank would trade the form with your bank for money which they would then place in the person-to-be-paid's account. It worked pretty well but was much slower (several days, at best) than our modern electronic system(s). :-)

== Michael

Thanks - would love to see that picture!

Well, here's a scan of the type and a few examples of how it might have been used. It's been years since I have seen a paper cheque that would have included such security type, so I'm not sure that I've got the format correct, but it's close enough to get the idea across.

The "multi-dot" key on the Olympia SG3:



Typing with the "multi-dot" key:



As for how many other keys don't exactly represent what is typed on the page, I would say it is most of them. Take for example, as Michael suggested, the dollar symbol. Look at what it looks like in the above type sample in comparison to what the key shows (below). This mismatch holds true for most of the keyboard.





 

Great domonstration of that key - thanks!

I tend to think the overstike is the intended function; alteration-exposing background, as others have suggested.

Also agree that no keyboard is an exact representation of the typeface printed on the paper - least, I have never seen one that is.  Given that manufacturers often offered several typefaces, you could not expect them to match the keyboard to any one of them.  And that may never have been the best thing to do anyway; indentifying the key you wish to hit is one thing, but reading words typed on the page is another, so it is natural that a different 'font' may would chosen for each job.

Thanks again for the photo.