Warchalking is a practice used to publicly indicate the presence of a wireless network in an urban area, either public or private. A basic system of symbols are used to describe the type of network ie. bandwidth, open, closed, WEP, SSID, distance and location. There are also more advanced symbols used, such as an eye to indicate logging, but these are not part of the core symbol group. These symbols are drawn on the street by warchalkers to promote the use of free wireless networks and to "enlighten" corporations with lax network security.

War chalking is closely related to war driving and war walking. It claims to have its roots from depression days when hobos would use a system of drawn symbols to indicate a place where a free meal could be obtained, presumably because not all hobos were able to read and write back then. (as opposed to now?)

It's a very cool urban art form in its infancy, set to become huge, with warchalking images popping up in every continent. Many major newspapers and magazines have also devoted many column inches to war chalking and wardriving.

Graffiti for geeks.

PDF of basic war chalking symbols: http://www.blackbeltjones.com/warchalking/warchalking0_9.pdf

The home of warchalking: www.warchalking.org