[James Birkett]

That looks like he's used a plug-in to replace his username with an image..

Try this:
Admin CP -> Plugins & Products -> Add New Plugin

Product: vBulletin
Hook Location: fetch_musername
Title: Username
PHP Code:

PHP Code:

if($user['userid'] == '{Your userID}'){
$user['musername'] = '<img src="path/to/image" />';
} 


This is untested.

If you give me your UserID I'll try and create it specifically for your forum.