[Dave]

PHP Code:

if($vbulletin->userinfo['userid'] <= 0){
   // Not logged in
} else {
   // Logged in
} 


If you want to do it in a template then it depends on the template, but generally something like

<vb:if condition="$bbuserinfo['userid'] <= 0">
Not logged in
<vb:else />
Logged in
</vb:if>