The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The package appears to be licensed under a Creative Commons license but only includes the human-readable summary in the debian/copyright file which is not the actual licence. The Creative Commons webpages contains the following disclaimer:
This deed highlights only some of the key features and terms of the actual license. It is not a license and has no legal value. You should carefully review all of the terms and conditions of the actual license before using the licensed material.
Creative Commons is not a law firm and does not provide legal services. Distributing, displaying, or linking to this deed or the license that it summarizes does not create a lawyer-client or any other relationship.
Please use the full, plain-text version of the license text which may be found here: