Those have pins in them.... probably 3/16" threaded rods, about 3" or so long. Make a pattern, drill the pattern into the wall and set the letters in them. You can also put some pads on them a little ways back, from the back of the letter to hold some strong adhesive. If you can get to the back side of the wall, you can double nut them. Be sure to waterproof each and every hole from the outside.