My orginal intention for buying ArtRage was to do layout in Graffiti Art style for a old garage in my back yard. It is long and I have often considered it for a great mural.
Your project if you should choose to accept is to create a "air brush & roller only" painting in Graffiti Art style. Use the airbrush on it's side, overspray, whatever mimicks a can of spray paint, and create some Graffiti Art.
Personal tags are acceptable, preferably something beyond the "toy" art stage.
PS. A link to inspire you.