This is the same JoelKatz as on the bitcointalk forums, currently Chief Cryptographer at Ripple Labs.
My (not nearly) well-known (enough) Bitcoin vanity address signing the message is:
"1Joe1Katzci1rFcsr9HH7SLuHVnDy2aihZ"
Message:
"09/30/15 JoelKatz(forum.bitcoin.com) = JoelKatz(bitcointalk.org ...