An interesting Guerrilla Marketing campaign by Condor Airlines in Europe. Many businesses in Europe shut down for a few hours at lunchtime or a few weeks in the summer while they are on vacation and need signage about being gone. Condor supplies these businesses with signs that roughly say "We have flown the coop" but have no mention of Condor Airlines, but mention the site "weloveflying.com" which links to Condor. Nice
Since American businesses do not really shut down at lunchtime or for a few vacation weeks, this would not really work in the USA though.