I painted this seal onto the back of my drawing notebook using watercolors. Two things I learned -- 1: cardboard may seem like it won't accept paint, but it does! and 2: ANY color you paint on cardboard looks A LOT darker than it will look when dry. This is true of most anything you paint with watercolor, but its even more true when the surface is cardboard.
This'll keep my notebook safe from those smudge demons and pixies that like to run rampant through my notebook when i'm not looking and make it all fuzzy and smudgy. ('course, a pencil fixative would probably work just as well (probably even better))