The tag is present in Lintian version 2.109.24. That is the most recent version we know about.
The copyright file contains the incomplete Debian packaging
copyright boilerplate from older versions of
(C) alone is not considered a valid copyright notice in some
countries. The word
Copyright or the © symbol should be used
instead or in addition to
Copyright notices like this are, in any country that's a signatory to the Berne Convention, not required to claim copyright on a work, but their presence may allow claiming additional damages should a copyright case go to court. If you provide a notice, you may as well provide one that's legally recognized in a broader range of countries.