Manual:$wgRightsUrl

Details
Set this to specify an external URL containing details about the content license used on your wiki. If $wgRightsPage is set then this setting is ignored.

In MediaWiki 1.8.2, it appears that $wgRightsUrl governs portions of the Creative Commons metadata generated within function wfCreativeCommonsRdf in file Metadata.php regardless of whether $wgRightsPage is set or not.