I use a china marker. It is more like a crayon type pencil, which you can pick up at any art store or Hobby Lobby. Degrease the area you plan to fill in using rubbing alchohol. Then rub the china marker back and forth across the area, and as it crosses the lettering/numbers it will fill in. Then use your finger to help fill in the numbers. The heat from your finger helps to fill in the numbers/letters. Then wipe off the excess on the surface, which will leave the white marker in the numbers/letters. Then... re-oil the surface.

"THIS WE'LL DEFEND!"

"LIFE HAS MANY CHOICES... ETERNITY ONLY HAS TWO!"