If you look at the first post of this
http://www.twcenter.net/forums/showthread.php?t=319378 SWhunter has a sparta sig, just right click it and copy, then if you look near the top of any page in the tw forums, you will see a line of things that say My account, Register, FAQ, Rules etc just below the bit that tells you what page you are viewing. Then click on "my account" and down the right hand side there will be a list of things, find the one that says "edit signature", click on that and then you can just paste the signature that you copied earlier.