I love GAC05's idea of the pressure washer actually blasting the name out of a grungy wall.
Maybe even a grungy sidewalk? Think about what work the client does mostly.. does he pressure wash the side's of houses more than he does parking lots, etc?
I'd sit down with your client and figure out what market he is trying to capture the most, is it corporate clients or residential homeowners who just need general pressure washing and steam cleaning... and then make a medium from there..
Just my 0.02 from someone who doesn't really know