You need to go into usercp (in the blue content bar above threads!) click edit signature and you can put whatever you want in the box, preview it and if you like it click save. to get a tracker you can go here
and just follow the instructions on how to make one , then right click (cut ) then paste it in your signature box!
If I've got it wrong (I'm not brilliant at this stuff) I'm sure somebody else will also tell you how to do it!