The tag is present in Lintian version 2.109.6. That is the most recent version we know about.
The copyright file for this package does not appear to contain a copyright notice. You should copy the copyright notice from the upstream source (or add one of your own for a native package). A copyright notice must consist of Copyright, Copr., or the Unicode symbol of C in a circle followed by the years and the copyright holder. A copyright notice is not required for a work to be copyrighted, but Debian requires the copyright file include the authors and years of copyright, and including a valid copyright notice is the best way to do that. Examples:
Copyright YYYY Firstname Lastname <firstname.lastname@example.org> Copr. YYYY-YYYY Firstname Lastname <email@example.com> © YYYY,YYYY Firstname Lastname <firstname.lastname@example.org>
If the package is in the public domain rather than copyrighted, be sure to mention "public domain" in the copyright file. Please be aware that this is very rare and not the same as a DFSG-free license. True public domain software is generally limited to such special cases as a work product of a United States government agency.
Please refer to https://ftp-master.debian.org/REJECT-FAQ.html for details.