12 Letters That Didn't Make the Alphabet.
When I was a kid in school and had to take extensive lecture notes from one of the worst teachers I ever had--our 7th grade Texas history teacher--I made up right out of my head symbols pretty much identical to "that" and "eng" so I could (in theory) write notes faster.
I also used a numeral "2" with a slash through it for "to" or "too."
He wasn't one of the worst teachers I ever had just because I had to take lecture notes all year long. He was one of the worst because he was ignorant and knew nothing about Texas history--getting all his information from some book he had taken from the high school library. The first time I corrected one of his mistakes, he gave me extra points. The second time he only grunted acknowledgement. The third time he told me, "Shut up, Peschke." After that I never spoke to him again.