Newly registered members are not allowed to advertise their own sites in signatures until they have a post of count of at least 100.
Your main signature image has a maximum size of:
130 (height) x 500 (width) pixels, with a maximum file size of 200Kb.
1 userbar is allowed in your signature, the maximum dimensions are 400 (width) x 20 (height) pixels.
2 userbars are allowed for clan leaders (one extra userbar to show their clan leader status).
Text in signatures is limited to 4 lines. Blank lines are also counted towards the text line limit. The max text size allowed in any signature is size 3.