From Sig To Noise: Misforgivings of the Mobile Signature. You can spot the novices immediately. Any expert emailer knows when to (and when not to) use a proper email signature when composing a mail. That automatic addendum that mail clients allow makes emailers both creatures of efficiency, and freaks of a sort, revealing personal datapoints to recipients without pause. Phone number, fax number, mobile number, home number, company name, job title, favorite inspirational quote—all at once. Most times, frankly, it’s a bit too much too soon.