In case you missed this (which I did), Fiat did an interesting image recognition campaign using street signs to promote their Evo. Users downloaded their iPhone app, and when they held it in front of various different street signs it showed further content. Hold it in front of a stop sign, there was a video and information about the breaking system. Hold it in a curve sign and it tells you how the intelligent headlights move around a bend. At the end of the information users were encouraged to book a test drive and the whole thing was incentivised with prizes.
How did it fare? Over 1 million people scanned the signs and most important of all, test drives went up by 82%. All that and on a tiny budget.