I sometimes had a very small piece of paper scribbled with stuff I couldn't remember while learning but turns out this way I knew what I had written down there and didn't need it afterall :D
One time I accidentally forgot about that tiny paper though and my teacher actually found it on some stairs and recognized my handwriting.
I used to do something similar, but writing it on my shoe (in pencil) so I wouldn’t lose the paper.
Mostly did it in my Japanese class in college because I didn’t have time to memorize vocab properly, but I never wrote the translations so I knew the info, it was basically a memory jog.