Sony have put up a teaser site on their official Japanese Playstation site today, Andriasang reports. The site only shows a man in the distance, walking alone through the desert, and the counter is (at the time of writing) currently standing at five days and 23 hours - which means that it should run out on Wednesday, June 1.
According to Andriasang, the meta tags on the site says "Discover the mysterious man who continues to walk in the desert." Who is it? The first theory that popped up in our heads was Nathan Drake, since Uncharted 3: Drake's Deception will largely take place in the desert. But your guess is as good as ours right now.