Here's an interesting idea from Saatchi & Saatchi Dubai. The financial crisis in Dubai 2009 had many expats suddenly receiving pink slips and their debts mounting as their paychecks vanished.
Fearing debt prison, expats fled the country, abandoning their fancy cars at the airport.
Thousands of abandoned cars were collecting sand-dust, when Saatchi had the bright idea of using them as ad space instead. They turned it around: thousands of abandoned cars
as people left Dubai - because people were using the Metro instead.
"I haven't left Dubai, I just love the metro!" "You'll find me on Metro Gold class", "I heart Metro" and variants appeared written in the dust on the cars. People liked the messages so much, they helped out adding to the campaign with their own variants. Clever!