His medium is his pen, and his canvas is the world. Whether it be a lampost, a bin or a wall, he draws on it if he feels there can be a humorous message conveyed through this mean.
I am not an illustrator myself, and do not aspire to be, however I do think what he is doing is very graphic. His work is of from a designers point of view, its so simple its genius. He literally creates a message out of things we see everyday, literally by giving it an additional meaning through a scribble with his marker pens.
check him out.