I think it is good to revisit this topic as it needs more thought as a methodology of urban geography. I came across this interesting blog post by Fiona Ferbrache on Geography Directions: http://geographydirections.wordpress.com/2011/05/10/urban-geography-a-flaneurs-encounter-with-graffiti-in-toulouse/ The author discusses her weekend stroll in Toulouse, France, her encounter with urban graffiti and her take on what it means to be a flâneur. She also mentions a recent article about urban graffiti by of McAuliffe and Iveson’s (2011). People are making statements in the city continuously. Graffiti is a message to the inhabitants of the city drawing them into contemplation to its underground element, its lack of color, and public art.
McAuliffe, C. and Iveson, K. (2011) Art and Crime (and Other Things Besides … ): Conceptualising Graffiti in the City. Geography Compass. 5,3. pp.128-143