I have made lots of tile art, coasters, sets that hang on the wall, 3-D Sculptured ones...
I use spray acrylic sealer on some of mine. For coasters I buy the clear mactac and cut a square to fit the tile - I like the mactac because it can be wiped clean, and it lasts for a long time. If you do use the mactac, be sure to cut the squares just slightly smaller than the tile surface, you don't want it to come right to the edge. (Mactac is like shelf liner only sticky on the back)
I have painted some with acrylic paint, sealed or mactacced those as well with no problems.
The absolute best and most beautiful effect for a tile is a temporary tattoo - once you apply it to the tile and seal it it becomes permanent and has a neat look because there is no discernible raised edge to the tattoos.
Suzan J

At Michael's Craft Store - ask one of the clerks for some help with your idea. Michael's has decals you could use for the initials for one thing. Not positive, but I think you could spray them with sealer after putting on the initial. That's why I say to ask the clerks, I'm not sure on that part.

Another idea is to look in the scrapbooking section for the initials or use a stencil. If you're going to paint them, I would use "enamel" decorative paint such as "Folk Art" paint. It's a good brand, thicker consistency. Look at the Donna Dewberry One-Stroke Painting books - the one for Glass Painting. You can cure enamel paint by letting it set for 21 days or baking it at a low temperature. It will explain it in the book on the first few pages. After it's baked or cured, you don't have to seal them and you can wash them without having to worry about the paint coming off. You can get the 4 X 4 tiles at places like Home Depot or Lowe's. They come in very pretty colors these days. You can purchase the cork for the backing at Michael's Craft Store also. I'd get a good glue to glue the cork on after you bake them, not just Elmer's Glue. Look at the description of uses on the back of a bottle of Modge Podge Glue, it's a better glue for projects. Some of the gals on the forum here use a glue called E6000. I've bought some recently but haven't used it just yet. They say it holds up extremely well.

Hope you'll post pics of them when you've finished, sure would love to see them.

Sal

Here is a link for making photo tiles from Splitcoast Stampers. I think they are really cool looking!

Here is a link that might be useful: Personalized Tiles

Suzan, is the Mactac you mentioned rather like a ModgePodge? (basically glue and varnish all in one concotion?)

Thanks! Ellie