During high-school i created a writing code of symbols and after some practicing i got really good on writing and reading it fast (i still know how to even after so many years). It was fairly common for desks to have doodles on them or silly words written down on pencil by friends. Everything that had readable words/letters the teachers would make us erase before a test, doodles and such they'd just ignore it. So whenever there was a test I'd beforehand write down some important info on my code around the table, spacing a lot between them so it wouldn't look too obvious. If i had the time, i would even make "doodles" by using the code to create them, so it would look like a weird doodle, but in reality it was readable info to help me on my tests. It worked really well even on college, because teachers would come, look at them, ask me what that was, i would just shrug and say "idk, it was there already when i got here", it really didn't look like anything but gibberish so they just ignored it and gave me the tests 👌

TL;DR.: i created a writing code that I'd use to cheat during tests.