Go to User CP top left. Choose Edit Signature. Scroll down to the ticker code that looks like this: "url=http://www.3fatchicks.com/] img]http://www.3fatchicks.net/img/bar-retro6/slider-but3/lb/196/145/196/.png[/img] [/url"
The 196/145/196 represents start/goal/current weight. Change the last 196 to your current weight. Save changes.