http://creativecommons.org/weblog/entry/40666

The Open Access Button "is a browser bookmark tool that allows users to report when they hit paywalled access to academic articles and discover open access versions of that research. The button was created by university students David Carroll and Joseph McArthur, and announced at the Berlin 11 Student and Early Stage Researcher Satellite Conference."

https://www.openaccessbutton.org/

Update:
http://infobib.de/blog/2013/11/19/start-des-open-access-button/