From the BBC:
Facebook has devised a "sympathise" button as an alternative to the "like" button for use in certain situations.
If a user selected a negative emotion from Facebook's list of feelings in a status update then the "like" button would change to "sympathise".
http://www.bbc.co.uk/news/technology-25299597
The article says that Facebook aren't planning to release it just yet, but the idea is there. It's similar to RYL's hug button. I think it's a good idea and hope it gets released soon.