That is correct, these signatures work using BBC Code.
To add an image, you first upload your picture to an image host such as tinypic, imageshack, etc. You then copy the direct link to the image. The format to have an image display in your signature is to do [*img]LINKTOIMAGE[*/img] Simply put your direct image link in between the img tags. As well, remove the stars from [*img] and [*/img] I had to put those there so they don't become tags and are seen as text to you.
