I too find this a little weird. How is email signatures gonna be used to exploit a hole? What hole. An email signature is most of the time just text or at most html. there shouldnt be any hole for them to exploit.

what alpha says could be it. using the info supplied to break in likephone numbers for wardialing. but thats not so much a hole as it is a user education problem. anyway, most of the time we use different sets of numbers for dial up access compared to the regular users tel numbers. also if you secure your network well then wardialing will not be a problem. even people without the numbers will try it anyway.