If Satoshi signs a message with the private key from the Genesis block and moves some Bitcoin from the same address, it could be strong evidence of his identity.  But I highly doubt he will never do that, he is not dumb to ruin his real life once he reveals himself and it could be he becomes subject to lawsuits, government regulations, or even criminal charges.

I would like to stop thinking that Satoshi will reveal himself in the future or there's a chance to reveal himself in public and brings solid evidence just to convince people.  Just respect his decision to remain anonymous, besides, without him, Bitcoin continued to succeed and be widely adopted in different countries.