if (!function_exists('ShowAd')) {
    function ShowAd($action)
    {
        $ad = <<<ENDOFAD
<!--Ad advertisement snippet, begin -->
<script type='text/javascript'>

stuff goes here

</script>
<script type='text/javascript' src='http://example/somepath/foo.js'></script>
<!--Ad, end -->
ENDOFAD;
        $action->raw($ad);
        return true;
    }
}