If you want to load yourself some waterproof ammo ... they sell some stuff on Midway to make it so. It's pretty much like fingernail polish, applicator and all.
Or you can just use fingernail polish; much cheaper and you get to choose the color.
I've been using fingernail polish on the primers of my reloaded ammunition since 1980 and have had no problems with it. No flaking, no residue, some color on the bolt face that is easily removed during routine cleaning.