You can scan your sketch into your computer, print it onto the decal paper and apply the decal to your tile(s). Once dry, the decal has a waterproof finish.
If you want someone else to do the work for you, here are two companies that put your artwork or photos onto tiles.
Morgan Home Accents uses a UV resistant imprint process that should last for years. You can mail or e-mail your photo or artwork. Production takes three to four weeks.
Change Your Art also accepts mail or e-mail images. They offer a variety of tile types with varying durability and characteristics. For example, they have glow in the dark tiles and glass tiles that are imprinted on the reverse for maximum durability.