Spray paint brushes:
https://www.brusheezy.com/brushes/1476-splatter
http://www.texturemate.com/content/spray-paint-drip-1-brush-pack-photoshop-or-gimp

In this tutorial I walk you through the process of creating a spray paint overlay material in KeyShot using the material graph. I’ll be covering how to add a material as a label, how to use an opacity map, how to create your own spray paint mask in Photoshop and why it can give you better results by blurring the bump map slightly.