List of mathematical symbols
en.wikipedia.org
en.wikipedia.org
* https://en.wikipedia.org/wiki/Latin_letters_used_in_mathemat...
* https://en.wikipedia.org/wiki/Greek_letters_used_in_mathemat...
* https://en.wikipedia.org/wiki/Aleph_number
* https://en.wikipedia.org/wiki/Beth_number
* https://en.wikipedia.org/wiki/History_of_mathematical_notati...
I don't think you mean that if you perform a series of transformations on the body of your message you will get Keith
I don't think you mean that your body of text is approximately equal to Keith, or Asymptotically equal to be precise.
I don't think you mean that your body of text is essentially the same as you.
Though all of these are somewhat close to what a signature means, I suppose.
I've seen the ~Name notation around a fair number of times, I assumed it was just a form of notation.
http://www.fileformat.info/info/unicode/char/299e/index.htm
P.S. thanks for the new term - steradians! It's amazing how many terms are in the mathematically universe :-)