Mask Map for graffiti

The base material is a simple red:

The opacity slot is NOT used. MASK is in the diffuse slot:

paint mark.psd looks like this ... the white area is wide enough to cover up any unwanted tiling of the brush stroke.

The result:

Note on the stack:

The bricks are applied with map channel 1 as a box, and the paint splat positioned with map channel 2 as a plane.