That is a signature graphic, you can go to your User CP (link found at the top of the page) and enter it under 'Edit Signature'.
If you do not have a graphic to you, you can have one made for you by going to this thread
and posting links to your pictures with the kitties names etc.
Once someone makes you one, it will be posted in this thread
for you to pic up, and if you need more help adding it to your profile, check out this