I'd love to know who he banks with - certainly isn't my lot and actually I doubt it's true of any other one - of course if it's your account you can cancel a standing order! (otherwise I'd still be paying money to my mum for board & lodgings when I moved out over 20 years ago...).
As for the signature, proof of ID etc, if they simply sent a charity form like the ones they print in the paper or online on charity websites off to his bank, they don't often need a sig. Also if they were quoting his account details and home address, then I doubt very much that whoever processed it at the machine room bothered to look at the signature. And I'm sure examples of his autograph are out there somewhere...
I hope he lets them keep the money.