I think a signature ban should be administered at a bare minimum. I'm not sure what the guy gains by putting the lie in his signature, but there is no reason to try and dupe the users of the forum. I hope you have reported him?
I think the signature ban is too mild a punishment for discrediting the forum administration. This
new admin deliberately undermines their authority with his behavior. I would suggest a permanent ban (if it was up to me), so that it would be a lesson for others and so that it would not even occur to others to repeat such a thing.