fixed it this code works and shows the alert image, hope you dont mind.
Code:
<if condition="$show[guest]">
<!-- Infobar -->
<link rel="stylesheet" href="clientscript/vbulletin_css/infobar.css" type="text/css">
<div id="info"><div id="infobar" align="left"><a href="register.php"><img src="images/alert.png" /> You are not registered yet. Please click here to register!</a></div></div>
<!-- Infobar -->
</if>