I found a folded up twenty dollar bill on the sidewalk once when I was a kid. At least I thought I did, it turned out to be a coupon. I was as pissed as a twelve-year-old could get until I realized I could prank my friends with it.
Stuart Elliott has a story in The New York Times (log-in required) on a similar effort for the Nissian Altima.
As the article states, "For the promotion, 20,000 key rings will be deliberately “lost” in bars, concert halls, sports arenas and other public places in seven large markets. Each key ring will have three keys, all real, and two tags. The biggest key resembles a car key and the other two look as if they could fit the locks on house or office doors."
The big tag reads, "If found, please do not return. My new generation Nissian Altima has Intelligent Key with push-button ignition, and I no longer need these.” The second tag directs the finder to a sweepstakes.
I like how well this relates to the product, but I think they missed an opportunity to create more of a mystery around the payoff.
The lost wallet thing has been done plenty, but at least this execution for a movie tried to build a story. I think Carlsberg had some fun with the fake passports they left in cabs and bars.
So I think such stunts can be used as engaging misdirection. But if the reward isn't worth the effort, it'll just erode trust in the brand.