Why do people sign their posts?

[Generic Villain]

Seriously. If you're posting under an alias and sign with your real name, that's one thing. Or if you include additional information in your sig. But what's the point of signing a post with the alias that already appears at the top of your post?

-Generic Villain

[Drejk]

I guess that for some people it is reflex for some from very old messageboards/mailing lists where the information wasn't clearly visible and everyone used signatures in their posts to be recognized.
For others it is a reflex from writing e-mails.
And the rest just likes brandishing their signatures.