Interesting figures out of researcher firm PQ Media this month on the size and growth of “alternative out-of-home” media, which includes video advertising networks and screens in theatres, offices, stores, in-transit, and other digital billboard locations. According to their research, the overall category grew 27% to $1.67B in 2006. Take those figures (which assumingly lump in other miscellaneous items) with a grain of salt, but there’s no denying that the proliferation of digital signage with advertising messages is happening.

Patrick Quinn of PQ Media said, “Ironically, the trends impeding traditional media — consumer fragmentation and control, advertising accountability and the emergence of digital technology — are the very catalysts stimulating the tremendous growth in alternative out-of-home advertising.” Much of the technology press attention on the digital media space (both mainstream and blog) has covered consumers’ consumption inside the home (web, digital audio and video) or on their own devices when they leave the home. Yet the availability of digital media has the opportunity to spread to the entire real estate of public life.

Is there a day in the future when property owners with public space, like shopping malls, become media companies focusing on selling not just physical store inventory but also ad inventory? It’s already slipping into the consciousness of these groups; for example, Simon Property Group annual report mentions their providing digital programming in their annual report with “very encouraging” initial response.

But what does this mean? Some people like John Blossom of Shore Communications have argued that media companies have become desensitized to the idea of public space, believing that any and all space is open for media or advertising. Is this really true? Next time you walk outside in public, consider the fact that there’s visual real estate inventory available wherever you look. But whether that perspective is beneficial for society is definitely an issue. Judith Perrolle, a professor of sociology at Northeastern Univ., has called coined the phrase “solid state spam” to label unwanted and unwelcome messages appearing in a public area, when marketers fail to consider or respect the community’s views of space.

But isn’t the notion of the social media revolution that media is supposed to accommodate consumers not violate norms? Don’t consumers have the ability to dictate the here, what, where, when, and why they consume media? Shouldn’t this notion extend to the public space as well?

On Thursday, the Taxi and Limousine Commission of New York approved a plan to install touch-screen monitors in their entire fleet of taxis. These screens will allow riders to pay by credit card, check on news stories, map out where the cab is going and find information about eateries and bars. To me, this example use of a public space for digital screen media seems more than appropriate – it delivers contextually relevant content to people who need it at that moment, and the advertising messages which follow are (presumably) relevant.

As outdoor digital signage continues to proliferate, we’re going to need some public discourse to reach a consensus about what is acceptable public real estate for these media. There are clear benefits – advertisers and consumers alike – for appropriate outdoor digital media as sources of useful information, and the business opportunities to serve this growing market are perhaps under appreciated.

(Thanks to Greg Peverill-Conti of Weber Shandwick who has helped me think about these topic over the past couple of weeks.)