WarChalking : No, it’s got nothing to do with War. WarChalking is the practice of marking a series of symbols on sidewalks and walls to indicate nearby wireless access. That way, other computer users can pop open their laptops and connect to the Internet wirelessly. It was inspired by the practice of hobos during the Great Depression to use chalk marks to indicate which homes were friendly. Check out this photo of a warchalk sign at a top New Zealand hotel.
Update : Just came to know that Matt ‘black belt’ Jones invented this concept.