You can use conditon

<?php 
    while ($row_settings = mysql_fetch_array($rs_settings)) {
    if ($row_settings['message'] == '')
    {
       //your message
    }
    else
    {
        echo $row_settings['message']; 
    }
    } 
    ?>

You can use conditon

<?php 
    while ($row_settings = mysql_fetch_array($rs_settings)) {
        if ($row_settings['message'] == '') {
            //your message
        } else {
            echo $row_settings['message']; 
        }
    }
?>