A method of writing something down before you forget, whether on a piece of paper or on your arm or hand. May also include calling your own phone and leaving yourself a voice message, or emailing yourself. Basically a self-reminder.
Roommate 1: Can you give me a ride to the airport on Friday? My flight leaves at 6.
Roommate 2: Yeah hold on a sec, I'm gonna write that on a sticky note, just for memory insurance.