To get avatars and signatures you can request one in the GFX Section or just get one from a different website. To post an image in signature simply go to the User CP and click Edit Signature and then wrap the Image url in this BBCODE, like so.
You must be registered for see images
and ofcourse don't forget to save. The following applies for avatar too if you were wondering and lastly I hope you enjoy your time in NB ^_^