How would you do this?

Model Railroader Layouts and layout building
1

This is a sign hand painted onto a rock face. They would hang people off the side of the cliff to paint the rock face.

Time has obviously taken it’s toll here as it’s faded.

So how would you do something similar on a plaster casting?

2

You could try and cut a stencil and airbrush it on.

Or you could make a square form and use it as a guide and hand paint it.

3

you can mask and paint the square then apply dry transfer letters and overspray it after masking the edge in a little. When dry pick off the dry transfer letters. Use a decal. Print it and sand the back thin before applying it.

4

I’d go with the stencil and airbrush recommendation above.