You mean your signature?

vB Code: [ img ]http://www.urlofpic.com/pic.imagefile[ img ] with no spaces.

HTML:

< img src="URL" alt="Alternate Text" >
Embed a graphic image in the document. Attributes: src
Specifies the location of the image.
alt
Allows a text string to be put in place of the image in clients that cannot display images.
align
Specify a relationship to surrounding text. The argument for aligncan be one of top, middle, or bottom.
ismap
If ismapis present and the image tag is within an anchor, the image will become a "clickable image". The pixel coordinates of the cursor will be appended to the URL specified in the anchor if the user clicks within the ismap image. The resulting URL will take the form "URL?m,n" where m and n are integer coordinates, and the URL will specify the location of a program that will examine the pixel coordinates, and return an appropriate document.

from http://www.ku.edu/~acs/docs/other/HTML_quick.shtml

With a closing < /img > without the spaces on both sides.