http://www.secadministrator.com/articles/index.cfm?articleid=26207
"This week, I encountered the relatively new trend called "warchalking," which is related to war driving. War drivers use chalk to identify buildings that run wireless networks. According to what I've read, four men sitting at a pizza parlor in London developed warchalking, after at least one of them saw UK Architectural Association students design an office floor plan on the pavement. One of the men mentioned that hobos had once used symbols to pass along useful information, such as identifying houses at which they could get meals. The four men then decided that they could use a similar technique to identify unprotected wireless networks."
