The New York Times covers "grafedia," a form of street art that transcends virtual and physical space.
Here is how it works: the person posting the piece of grafedia uploads an image to the grafedia site ( and chooses a word to associate with it ("here"). That person then writes the word in a public place (street, print media, Internet) and underlines it in blue (the mark that distinguishes grafedia from graffiti; a full e-mail address is also a tip-off).

On the other end, when people see the writing and recognize it as grafedia, they send a text message or e-mail note to the appropriate e-mail address (the underlined word plus, or in the East Village example), and are sent the image.

Link (thanks, Susannah)

Reader comment: dan winckler says,

Yellow Arrow is a "Massively Authored Artistic Project" where anyone puts a yellow sticker next to something they find beautiful or interesting and submits it to the website. When someone sees the arrow, they can text message a number on the arrow and get the description the 'archer' applied to it. It's a lot like the grafedia project you posted today but deliberately non-destructive, that is, the arrows are easily removable and you're encouraged to ask permission from property holders. One of the creaters of the Yellow Arrow Project spoke at Dorkbot NYC last night, which I attended.