First, you can make one with a picture program of some kind. Or someone can make one for you. To get the signature under your name, here are two threads with instructions. This should help.
POSTING PICTURES on Pet Talk; class 101

and you can also look at this:

To put a picture in your signature, you need to click on User CP.

^User Cp

Then you will see a screen like this:

You need to click on Edit Profile.

Then this will come up:

The arrow is pointing to where you need to type in what you want in your signature. If you want the picture to show up, as you can see you need to type, [7img] [7/img] (without the sevens) with the URL in the center.

I hope this helped!!