Signatures are accessible from your profile.
After getting into profile look near the top of the page to the right and you will see categories, click on the one that says "signature"
To just use text, you type in like you would normally. To use a image you need to post it using the image format such as this:
(IMG)http://(insert the URL that is hosting your picture here)(/IMG)
The hosting site, such as photobucket will have it all set up all you all you have to do is choose how you want to display your image and copy the link then paste it into the signature box.
If anyone wants a custom signature made, please send me a IM with details.
Thanks,
Kobe