Okay, you obviously know how to add stuff to your signature that is where you'll be doing this.
Go to this page and right click and save one of these buttons to your own computer. We prefer you choose a small one.
In the 'edit signature' page add upload the button by clicking browse and finding it on your computer.
When it's added click the button to select it and then click on this link - - and paste or type the URL of your Rav page into the box.
Save and close.