to add the icons to the node titles i edited node.tpl.php
admin > theme_editor > edit jyo > edit node.tpl.php

So we want to make an icon show up on the left side of titles that are filed in the "audio" category. In node.tpl.php categories are in $terms. So I searched through $terms using preg_match(/audio/, $terms) in an if statement. See the code to see what I did, very easy hack!