As I received it:
The Washington Post's Tom Toles Cartoon Caption Contest returns today. To enter, check out what Tom Toles sketched and post your suggested caption in the comments section by 11:59 pm ET June 6. Toles will read through all the entries and will plan to announce the winner the next evening. The prize is a print of that cartoon, signed by Toles and including the caption suggested by the winner.
For the cartoon and official rules: http://www.washingtonpost.com/blogs/tom-toles/post/tom-toless-cartoon-caption-contest-returns/2011/05/27/AG7a9zCH_blog.html