oh, I guess you could use a macro to find out if it is upload or not....
<a href="%item-url%" class="messageimagelink"><img src="{.if not|{.get|can upload.}|**YOUR ICON**|/template/icons/folder.gif.}" class="noIcon" alt=""/></a>
But I am unsure if 'get' works outside the folder for upload, and I think the icon wont show unless the user is logged in so it can detect that they can upload.