You need to drill through the plaster and into the wood framing.
How to hang a wooden sign on wall.
How to hang wooden letters on a wall.
After you slide the artwork on the wall mounted cleats predrill and drive some long wood screws into the sides of the bottom cleat.
Line up the sign and mark for screws before attaching as outlined above.
There are a number of different ways to hang the letters up meaning you.
Use drywall screws to drive through the sign into the wall.
Hang larger signs with screws through the face.
Line up large signs with studs for added security.
Locate and mark the studs.
The hardness of brick complicates the installation of a sign on a brick wall.
Most wall framings set studs every 16 inches so you should be okay to measure from there but double check with a pilot hole.
Do this for both the top and bottom cleats.
To the upper cleat attach a 1x1 or 1x2 strip of wood that is 5 1 2 long so that it s flush to the top of the cleat on the artwork.