Signed message or this is just another PR stunt for whatever the reason this man may have.
I call BS and all future Satoshi-wannabes who are not able to sign a message or talk themselve around doing so.
a signed pgp message is one thing..
but something that would cause controversy is not the identity of satoshi. but if satoshi still has privkeys of addresses from january09-summer09
and annoncing that just 0.1btc will move from an early address on christmas day (pre-announcing it) and then actually doing it on the day.. well that would solve any speculation that the early funds are or are not lost to oblivion