Try this code in your logo_sidebox_defines.php
HTML Code:
define('LOGO_SIDEBOX_LINK', '"http:///sealserver.trustwave.com/cert.php?customerId=w6oj3BZ9ZhnnLcVNVXtmgytnQ66qDb&size=105x54&style=" rel="external" target="_blank"');//only if you want to open in a new window
Let me know if this gets you on the right track...