It's not working and what is the point of posting this code if we can't use it until you make an better one? (The _ is part of the user name)
<script>
function custom_message(){
//Created by Agent Moose (smcodes.smfforfree3.com)
var message = new Array();
message[message.length] = ["Phoebe_Jordan","Whatever..."]
if(location.href.match(/topic/i)){
for(f=0;f<message.length;f++){
$("a").each(function(){
if(this.innerHTML == message[f][0] && $(this).parent("b").parent("td").html()){
$(this).after("<div class='windowbg2'><span class='smalltext'><b>Custom Message:</b><br>" + message[f][1] + "</span></div>");
};});};};};
custom_message();
</script>