Update:
Here's another way to look at it - when you're editing your Signature, and Previewing your changes, the bottom of the sig box should not be lower than the bottom of the "box" framing "Pictures & Albums" in the menu to the left:


Edit: If you have a combination of text and images and have run out of vertical room for your sig, but have room horizontally, send me a PM and I can help you format it to take advantage of that horizontal space, like mine.