I mark up maps that I've printed out. Mostly with coffee rings, but some of the notations still make sense to me.
When it comes to reading my own penmanship, sometimes the coffee rings are actually more legible. :wink_smile:
I keep notes on characters in small notebooks. I also use a map marker mod, which allows me to leave "notes" about locations (as well as adding markers for more locations than the vanilla map shows.)