I live in a house on a concrete slab. I noticed after showering that there are two tiles on the floor of the bathroom that are warm. I checked again this morning before using any water and the tiles were not warm, but after showering they were warm again. Does this mean I have a leak in the pipes in the foundation?

No. At least not necessarily. Heat is just transferring up through the pipe and the concrete.
Floor radiant heating systems rely on this principle.

It doesn't sound like a pressure leak and that's a plus. But I do think that there's a leak in the drain system. I can't buy the transfer idea. If we were possible to transfer heat from the drain system through the dirt and cement we would have to place like this all the time.
Since it's just the drain system and not a pressure leak you can just let it go unless it bothers you is with chase the pounds will have to come up in the slab opened up to repair the leak. Your choice. What's your pleasure? Good luck, Tom

I checked the water meter when no water was on in the house and it wasn't moving. I turned on a faucet slightly and checked again and it was spinning. This is a good sign, yes? The warm tiles are about two feet in front of the commode and the shower is about another two feet in the opposite direction. Should I be concerned about sewage draining? If we don't repair it will it cause damage to the house/foundation? I really don't want to tear up the slab. Advice?

Maybe since it's just two warm tiles, the drain is close to the surface of the floor for a short distance, speedball?

I think I would get a couple buckets of hot water and pour down the shower drain to determine if it is a supply or a drain problem.