This is very easy, you're just a few clicks away.
- Click on thebutton at the top of the forum (under the site's banner)
- Now click on the Signature link.
- Enter the signature you want to have shown at the end of all of your posts, then click the Preview button to see if you like the way it looks.
- When you have your signature the way you want it, choose the Save button, and you're all done~!