Click on "My Controls"

-------------------------------------------------------------------------------------------------------------
Step2:
Click on "Edit Signature"

-------------------------------------------------------------------------------------------------------------
Step3:
Add your picture using img tags for example;
[img]http://www.mywebsite.com/mypicture.jpg[/img]
Or if you want your picture to be a clickable link;
[url=http://www.mywebsite.com][img]http://www.mywebsite.com/mypicture.jpg[/img][/url]


Possibly a sticky guide for this section?