A great piece on who pointless email signatures are:
[Email disclaimers] are assumed to be a wise precaution. But they are mostly, legally speaking, pointless. Lawyers and experts on internet policy say no court case has ever turned on the presence or absence of such an automatic e-mail footer in America, the most litigious of rich countries.
Many disclaimers are, in effect, seeking to impose a contractual obligation unilaterally, and thus are probably unenforceable. This is clear in Europe, where a directive from the European Commission tells the courts to strike out any unreasonable contractual obligation on a consumer if he has not freely negotiated it. And a footer stating that nothing in the e-mail should be used to break the law would be of no protection to a lawyer or financial adviser sending a message that did suggest something illegal.