Warchalking was the practice of drawing chalk symbols on a pavement or wall to tell other people that there is a wireless Internet network nearby, and whether it is open or locked. A pair of half-circles back to back meant an open network you could simply join; a closed circle meant it was protected. It started in London in 2002, borrowing the idea from the secret chalk marks that homeless travellers once left on gateposts to tell each other which houses would give them food. So it was half a practical tool, half a piece of street art and a joke. It never became widespread, and it died out quickly once nearly every café had free Wi-Fi and everyone carried mobile data. Today the word is a small piece of Internet history; you meet it in vocabulary lists and in articles about early Wi-Fi culture rather than in real life. It is often mentioned together with 'wardriving' — driving around a city with a laptop looking for open networks. Both are 'grey' activities: making the chalk mark is not itself illegal, but joining someone else's network without permission usually is. The word can be a noun ('warchalking was popular for about a year') or you can talk about someone who 'warchalks' a location, though that verb was always rarer.

無線網路粉筆標記；在人行道上用粉筆畫記號、告訴別人附近有無線網路可用，2002年左右的做法，現已消失