In more detail:
If you get an email from someone in legal or sales, it's almost guaranteed to have a long signature at the bottom. This signature will contain their full name, mailing address, phone number, job title, and - surprisingly often - an image of the company logo. The email is virtually guaranteed to be HTML and may even include background images.
HR's better, in my experience - you won't find background images, but you will, often, still have a company logo.
Geeks will sign their emails with their name. First name. Almost invariably with one or two dashes before it. Like, say, "--Bob" or "-Jeff". It's also worth pointing out that they will type this signature into every email of theirs - I haven't met a geek here for a while that used their email client's signature feature.
Why is this? I dunno. Theories: Geeks don't want to be called, just send an email reply. If you do have the right to call us, you can probably get our phone number some other way. Maybe part of it is that we trust the email headers - if it's not malicious email, the email headers will be right, and there's no need to make it redundant. Or maybe it's just a dislike of clutter. And part of it might be that we're used to changing programs, and tired of retyping signatures, so we just treat the email editor like a glorified text editor and leave it at that.
Meanwhile, on the legal/sales/HR side of things, they want people to be able to call them. They want to make it as easy as possible for others to get in contact with them, in any way possible. And chances are they don't change computers or software often, so they can just leave it in their signature file and be done with it.