Another way, is to put single stars one either side.
Code:
<img border="0" src="images/star.gif" width="10" height="11"><b><font size="1">Contributor</font></b><img border="0" src="images/star.gif" width="10" height="11">
Looks like this on my board:
Attached below is the star I made for it. Just drop the image into your forums images directory and replace your postbit_donation text with the above code.