I have never seen something like that. It's just javascript, you can see it in the source code:
HTML Code:
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<img alt="." src="/forums/images/blank.gif" width="0" height = "11" hspace="0" />
<a href="http://www.shroomery.org/forums/showflat.php/Cat/0/Number/4546706/an/0/page/0" onmouseover="m(this);getBody('4546706')" onmouseout="delayHide()">Welcome to the Trip Reports Forum! (Rules, Suggestions, Etc.)</a>
</td>
So, I'd go take a look at his javascript and then you are halfway there. The other part is to grab the message in the query.