Well, you know the code that is in the box. Well, copy and paste it into your sig (sometimes the box will also be copied, so just "Backspace" before the entire code a few times until it is gone). Replace the image URL (which is in the background-image:url("right here"); and replace it with the image you want, and the --- should be deleted also). To get the height and width, right click on the image to see the properties (or, I think it is only on Firefox), and type what it says. And, for your image in your sig (WH banner) has 430px of width, and 180px of height. If you get confused, I can make it for you, and you can look over how I did it.