When to Use Your Email Signature for More Than a Sign-Off The email signature can be a powerful marketing tool -- but it can quickly become an irritating vehicle of self-promotion.

Two years ago, Alaia Williams used a run-of-the-mill email signature: title, company, phone number. But as an online business strategist, she wondered if she was overlooking an obvious opportunity. So she started adding to her signature, piece by piece.

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She placed social media icons to link to her Facebook, Twitter and LinkedIn accounts. She added a sign-up for her mailing list. She even threw in a head shot and info on her product line. The results? Her followers and opt-in rates immediately increased. "I'm getting inquiries and referrals from people who don't even know me well," she says. Williams' instinct was spot-on, it turns out. Email signatures are no longer just an afterthought; they're a valuable marketing opportunity. That's because they typically come from a trusted source (or at least a professional acquaintance), and because getting a work email is a fundamentally different experience than, say, watching TV or scrolling through Twitter.