>>13812920My first thought was a change-the-URL riddle game, but you mention posters advertising it, so I'm 99% certain it's a CPA (cost-per-action) campaign where someone will get about a buck for every email entered into a form somewhere and maybe added to a mailing list for targeted marketing at the "bored and disillusioned with life" types (think of the TV series Dispatches from Elsewhere).
I used to see these kinds of poster campaigns discussed on
blackhatworld.com, a very popular site for blackhat SEO and outside-the-box money-making ideas.
