First, click on Edit Profile.
At the top of the screen, you will notice a tab marked "Create VGChartz Sig." Click on it to arrive at a new screen.
You will find a tab next to the words "Available Sigs." Click on it. That tab contains all the VGChartz sigs you can use at the moment. Select whichever one you like best. It will bring up a blank sample. If you don't like it, choose another.
If you're satisfied with the design, you can now scroll down and change the size, style, and color of several variables. Play around with it if you want, or leave all of them at their default value. Click on the "Preview" button, on the bottom of the screen, to see if you're happy with the changes you've made. If you're not, you can always click "Reset" to start from scratch. Once you're done customizing, click on "Get Code."
This brings you to a new screen. Simply copy everything in the "Forum Code" box, and then, when you edit your sig,* paste that code in. And that's it!