At a bus stop in Seattle, in blue chalk on the sidewalk, is a mysterious scribble: firstname.lastname@example.org. The cursive e-mail address is underlined in blue - a signal to passersby that they can use their cellphones to text message the address and receive a response. It is like hyperlinked text on the Internet, only here a phone, not a mouse, can "click" on it.
Graffiti artists are said to "tag" buildings, and practitioners of high-tech graffiti tag their e-mail address in blue underlined writing or on a distinctive yellow arrow to indicate their presence.
What people see when they type in the address posted on the wall or sidewalk ranges from the artistic - haiku and photography - to the practical - travel recommendations and advertisements. It's like a hidden code that links a person with others who have passed that way.
Graffiti, though illegal and considered a nuisance by cities, nonetheless remains a feature of urban life. In some quarters, tagging is viewed as a form of expression in the hands of artists. Grafedia - hyperlinked text on real surfaces - follows the same urban grass-roots traditions, though it may yet be co-opted by commercial interests as an advertising vehicle.
Grafedia has become more popular than its creator imagined when he launched the project six months ago.
"With Grafedia, I saw that the Web was going away from people's laptops and computers and more toward being ubiquitous," says Grafedia founder John Geraci, a graduate student in interactive telecommunications at New York University. "I wanted to do something that was an extreme version of that model, where you did away entirely with the idea of laptops and computers and sort of set the Web free to run through the streets."
Mr. Geraci has hit on an idea prevalent today - that the line between the natural and virtual world is largely artificial, and that the Web is in fact all around us, not just on our computers.
"People a generation from now will look back on how we viewed the Internet being something you went to use as very quaint and simplistic," Geraci says. "We need to embrace the idea of interweaving the physical world around us with the virtual world, not in a way that's virtual reality but in a way that's augmented reality."
Another company that facilitates high-tech graffiti is Yellow Arrow, which concerns itself with questions such as: When does an object become art? What makes a landmark? Who says what counts?
By providing a name and address, anyone can register at yellowarrow.org and order arrow stickers through the mail. Each arrow contains a code and a phone number. As with Grafedia, people can stick the arrows anywhere (their front doors, their jackets, their bumpers) and upload a file to the website, which anyone can access via cellphone or the site. Even travel guidebook "Lonely Planet" has caught wind of the project and encourages travelers to leave a trail of stories in the form of arrows wherever they go.
A Toronto project called [murmur] - complete with brackets - uses the Grafedia and Yellow Arrow concept of tagging specific landmarks, but in this case storytellers record little pieces of history about various parts of the city that passersby can access by dialing the number at the tagged location. (The project is expanding to Montreal and Vancouver.)
"These stories are an absolutely essential part of us feeling a sense of belonging in a place," says Gabe Sawhney, cofounder and producer of [murmur].
Mr. Sawhney isn't concerned about the potential for such projects to further clutter the public domain. "Urban spaces are wonderful because of the clutter," he says. "Posters, stickers, and graffiti are forms of democratic urban communication. Contrast this with advertising, which is a hugely undemocratic, imposed form of urban communication."
Meanwhile, advertisers are beginning to see potential in this new realm of unfiltered public interaction. If projects such as Grafedia generate mass appeal, advertisers may opt to hyperlink their billboards as well, says Eric Anderson, an expert on Web-based marketing for White Horse in Portland, Ore.
"The overall trend in marketing now is toward what I'd call 'contextual marketing,' where advertising can be anywhere," Mr. Anderson says. "That makes people uncomfortable, because any space can be co-opted. But Grafedia takes power away from these mass-media vehicles, where people begin to feel inundated, and puts it in places that are clever or exciting or interesting. It's a lot less pernicious."
New York artist Christina Ray, who studies psychogeography - the effect of space on human behavior - takes the concept further. At first, she played around with her own Grafedia tag. Now, she's working on a new project, Found City, with Geraci. "The idea is that you just go out with your cellphone and bookmark your city," she says.
"We're still trying to see what we can do," Ms. Ray admits. But it's clear that people are looking for new ways to use their cellphones and to fill in-between moments - such as during commutes. "It's almost like a third space, an intermediate space, and people are paying attention to what we can do in that space."