Warchalking Symbols If you see these symbols on the sidewalk in front of your home, they haven't been drawn by your local gas utility :-). You may be sharing your wireless internet connection!

Warchalking - wikipedia.org
Warchalking is the drawing of symbols in public places to advertise an open Wi-Fi wireless network.

How Warchalking Died
The purpose of this article is to explain how Warchalking has become obsolete. It is being replaced by Wi-Fi Zones that are being fueled by home networks, corporate networks, and even payphones.