You can use the [ img ] [ /img ] code to add an image. You put the URL (http://www.....) of the location of the image in between. No dynamic images, only jpg, gif and png.
Plus, the image should be rule-compliant:
While we allow the use of images in signatures we ask users not to abuse this privilage. Signature images should be limited to one or two and be no larger than 500 pixels by 100 pixels IN TOTAL [ie. the size of all signature images added together] Text signatures should also be no more than 5 or 6 lines long. It is unfair on some of our users to force them to download other peoples signatures that are longer than the average post.
You are not allowed to use that image extension on this board. A valid format is: [a href=\'http://www.domain.com/picture.gif\' target=\'_blank\']http://www.domain.com/picture.gif[/a], an invalid format is: [a href=\'http://www.domain.com/picture.one.gif\' target=\'_blank\']http://www.domain.com/picture.one.gif[/a]
It's fine by me. I dislike large size images in dimensions. I'm on broadband so that gif doesnt bother me but if the filesize is massive I doubt others would be happy downloading it every time you post