How to verify ASICMiner share ownership through Bitcoin address / blockchain.info? How do I verify ownership of ASICMiner shares through a Bitcoin address given that matches with a signed message I've been sent?
Go to https://blockchain.info/address/16fuoinLFjBmiCYmCYDXPNfERJtdPB5ASe

Check if the same address as he has signed the message with is on that page. This will only tell you that he had the shares the moment the dividend was paid.

Or you can ask friedcat on bitcointalk.org to confirm the ownership of shares.