Fountain of Knowledge

You'll need to add a new item to your portfolio and it will be an image type. The layout is simliar to when you add a static item, but at the end it will give you the option to uploade the image from your hard drive. after that, you'll get an item number for your image. Use that and instead of linking to it in your sig block like you would with an item, use the image tag. So if your item number was 1234567 your signature block would link to it like this:

{image:1234567}

Let me know if you're still having trouble