You need 100 posts before you are allowed an graphics sig.
Computer Forums - Announcements in Forum : Building, Buying, Upgrading for General PCs
Registered Users (0 -39 posts):
* Only forum provided avatars (currently being added)
* Profile pic, 100x100 & 62k
* Forum titles
Registered Users Extra (40 - 100 posts):
* Same as above
* Signature allowed, text only (according to the rules)
* Custom avatars allowed, 80x80 & 20k
Registered Users Extra BST (100 - 249 posts):
* Same as above
* Custom avatars allowed, 100x100 & 27k
* Graphics and text sigs allowed, maximum size of 300 x 100 & 20k (accoding to the rules)
* Buy/Sell/Trade forum available
Registered Users Extra 2 (250+ posts):
* Same as above
* Custom avatars allowed, 120x120 & 30k
* Graphics and Text sigs allowed, maximum size of 600 x 150 & 30k (according to the rules)
* Custom forum titles.