Now, it's gone. I think it's your preferences. If you are using the "Fast Reply" feature, look at the two check boxes underneath the textbox. You'll see "Quote message in reply?" on the bottom left and "Show your signature" on the bottom right. That's the one that you might have accidentally checked when making your post. You can also find it under "User CP" for your preferences as well.
I'm gonna un-check my "Show your signature" for this post. You'll see no signature.