Stippling is the creation of a pattern simulating varying degrees of solidity or shading by using small dots. Such a pattern may occur in nature and these effects are frequently emulated by artists.
With regard to sign painting, stippling is how we use a stiff short bristle brush. Rather than painting with strokes we push the tips of the brush directly into the wall almost as if we were using a hammer to apply the paint. The stiff brush holds up to this method of painting, and works well on a rouch surface where paint must be forced into nooks and crannies.