"What the caterpillar calls the end of life, wise men call a butterfly."

Chances are you've driven by them a zillion times but, like most symbols, they only have meaning if you understand them in their context. They aren't graffiti. It's warchalking!

Like the old hobo markings or urban art, they're sending you a message. In this case, they're telling you that you're in a 'hot spot' or an area that's covered by a wifi (or wireless network) connection.

In the spirit of the early Freenets, some people are advertising that you can connect to the Internet via their wifi connection free of charge.

That's really cool!