Re: IBM 1620 invalid character symbol

The only font on that machine can be found by feeling the key strikers in the typewriter.

In that context it's worth remembering that there while you could say for most typewriters that "the typewriter is the font", there were noted exceptions. The IBM Selectric, for example, had exchangeable type balls which allowed both a font and / or encoding change. (Encoding understood here as association of character to key).

That technology was then only two years in the future.

Other typewriters used interchangeable type wheels for the same purpose, but I believe that generally came later.

A./