Stud-mount lettering on Exterior Wall Tile

Porcelain & ceramic suck to drill. I would recommend tape-mounting them if that's feasible.

If you wind up drilling, you'll want a diamond core bit. Milwaukee's are decent and are available at Home Depot. Sometimes I use the diamond core bit to get through the glazing then use a glass & tile bit to get through the rest. Keep the bits cool with water.

 

I haven't had much trouble with a sds masonry bit and a hammer drill set to turn only. Yes quote extra though. Unless it is the worlds coolest contractor in the world, he's gonna lose his shirt on you if you crack any of them...
I had a job doing the same thing but with 'fabricated stone' or something like that. It was fake rock that chipped easily but drilled very nicely after you had a hole started. In any case, we got with the contractor and asked for a scrap of the material and did some thorough test drilling in the shop before install.

 

and be sure to tell them the wall will look nasty if the letters are removed

 

As Moze said, use a diamond core bit and you won't crack the tile. Porcelain is hard so it may take awhile. I usually bring a spray bottle with water to keep the bit cool. Once your through the porcelain you can switch to the appropriate bit depending on what is behind it. My guess is concrete but it could be hardie board.

 

Absolutely 100% diamond bit. It's way easier if you have someone with you to keep your bit cool by spraying a stream of water on it. Definitely switch to another (appropriate) bit once you're through if you can. I would also recommend practicing a couple times on some tile so you can get the hang of it before you do the real thing. You don't want to skate a diamond bit across some fancy tile.