What you are looking for is the BBCode, which will look like this:
HTML Code:
[url=http://lilyslim.com/][img]http://swtc.lilyslim.com/sis7bbw.png[/img][/url]
(Notice that it does not have any < or >, but it has [] instead)
Then you go to UserCP(Top left) and then go to "Edit Signature" which is in the menu to the left.
Let me know how you get on!
Below is a useful link that will show you step by step how to set up a weight ticker and put it into your signature.
http://www.minimins.com/tutorials/19...ctory-com.html (How to setup a weight loss ticker on Tickerfactory.com)