So you people might have been wondering, why the **** doesn't it allow me to have a signature?
To make it work for you, you should go to User CP (near the pm and logout tab)
And go to 'User Preferences', scroll a bit down, and you'll see: Always use my signature.
Make it say yes, then scroll down and save (send) the options.
You can now upload a signature and it will display on the forums!