That and a steady hand. I am certainly seeing that the brushes are very well loaded, lubricating the brushes as they move allowing for an almost frictionless movement.
Anyho, this may be of interest to you:
http://vimeo.com/61006621The movie is on tour - but sadly nowhere near me. I’ml be hoping it’s out on BluRay or some other High Def format for me to watch (if we are very lucky, the BBC may screen it as part of the Imagine series, like the did the Helvetica movie). The lack of London based venues has annoyed a few people I know.
http://signpaintermovie.blogspot.co.uk