Technology company Cisco Systems expects the market to top $3.6bn by 2011, and it hopes to capture about $1bn of that. Meanwhile, consultancy NSR forecasts DS networks will generate $2.7bn in ad revenues by 2013 and predicts that the number of sites will grow from 210,000 in 2007 to 850,000 worldwide by 2010.
Estate agents, travel and betting shops, mobile phone outlets and pubs have all quietly embraced the technology. Beyond retail there has been even more activity, with sales to corporate users, resort hotels, education and visitor centres rocketing.
Public transit systems are also popular, particularly for traditional news broadcasters attempting to follow an audience on the move. BBC News 24 dedicates a feed to urban centres such as Liverpool, and Sky News targets major stations.