Warchalking is a grass roots effort to create a standard iconography for public Wi-Fi access. The movement was started during the summer of 2002 in London by information architect Matt Jones, who posted and promoted the idea on his Web log (blog). The concept of a Wi-Fi iconography was inspired by the chalk markings used by hobos during the Great Depression to communicate information to fellow itinerants about the friendliness of a place or its inhabitants.
Creator Matt Jones began by posting three possible warchalking symbols on his blog. Two semi-circles back-to-back would indicate an open node, a circle would indicate the presence of a closed node, and a circle with the letter "W" inside it would indicate a WEP node. Ideally, each symbol would be chalked with a corresponding SSID next to it which would act as a password to the node.
Because chalk markings are temporary, warchalkers hope to avoid legal fines for defacing public or private property. The name warchalking is derived from the cracker terms war dialing and war driving.