With an avitar:
Go into your profile at the very top portion of the screen. Scroll down to the bottom and there you will see avitars. Now you may do any of the following: Upload an Avitar from ur machine or get one off of another site and link it here.
All Avitars must be its width can be no greater than 150 pixels, the height no greater than 150 pixels, and the file size no more than 49 KB. With that said I would find a picture or something online or maybe create one your self. Set it to these parameters in Paint and then save it. Come back on this site. And go to upload avitar from your machine. Click browse. Then find you pic. Hit open and you're done.
Pretty simple.
As for Signature images.
Check out the posts in the Board Suggestion forums and The Misc:
<a href=
http://board.ghostbusters.net/viewtopic.php?t=33>How to get your sig pic up</a>
If you need a pic of some kind Im sure I could find it for you. Just PM me or e-mail me.
-Matt