Easiest way to get the most realistic shot: Get a bright projector.
If you must do it in post there are several ways to go about doing it. If your camera doesn't move (tripod is your friend), it's going to be a lot easier. If the camera is moving, you'll have to do some motion tracking.
Basically, create your text layer, position it and distort it so that it matches the perspective of the wall. Use a the footage (or a precomp of the footage with some color correction effects applied to bump up the contrast) as a map for the Displacement Map effect so that the letters kind of bend a bit with the contour of the building. And use overlay or some other blending mode for your text layer. Which blending mode you use will depend on your footage. You may need to play with multiple copies of your text layer and/or varying the opacity of it.
If you have anything cross in front of the text, such as passing vehicles or people, you will have to rotoscope them out.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
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