There are only 400 Sumatran Tigers left in the world. To create awareness about this issue DDB worked with Portugal, The Man to create a song called Sumatran Tiger.
The song was lathe-cut onto 400 custom poly-carbonate records designed to degrade after a certain amount of plays. Leanr more about the project here.
Supposedly there are no other copies of the song. Unless you use the #EndangeredSong where you'll find it hidden on sites like SoundCloud, Reddit, Myspace, etc. then the song will go extinct.
Nice, insightful idea. Although with music piracy such as it is, and with the half a second it took me to find Portugal, The Man's complete discography on a pirate site just now, it may not be the best metaphor.