There's a thread on here somewhere that gives step by step direction on how to add the weight loss/BMI tickers to your signature.
You can get them at
Graphical Tickers and Trackers: Weight Loss, Trying To Conceive, Pregnancy... as well as at some other sites. Open a new window to go to Ticker Factory, and then after you design your ticker, you can copy it by right clicking on it. Then go to the "User CP" on this site (it's over to the right on this screen) and then to edit signature on the left side of that screen. Then paste in what you just copied into the signature box. Hopefully that will work.
Bookmark the Ticker Factory page when you get done designing your ticker, and then you can go back and edit it as you lose weight.