Until someone can provide some sort of cryptographic evidence (sign from an early address, moving coins, PGP, etc.), then what they say can be rightly ridiculed. If they can provide such evidence, then that doesn't automatically make them Satoshi, but it does warrant further discussion and examination. Signing a message proves ownership; it does not prove identity.
In fact, there's technically
nothing that could ever prove Satoshi's identity. Signing from early addresses or Satoshi's PGP key would only muddy the waters. Private keys can be compromised due to security mistakes or even encryption vulnerabilities.
I believe that
anybody claiming to be Satoshi ought to be ridiculed and ostracized from the community without question. It's an unprovable claim; believing it requires faith. That's the antithesis of everything Satoshi ever imparted to us, including the Bitcoin software. I'm not going to believe something I cant verify.
I think it would have to be the Genesis block rewards wallet to have any merit at all, if that was compromised the all of Satoshi's wallets could have been and if you have access to all of those wallets, you have some power at least as a whale.