The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
The Debian diff or native package contains files in a .hg
directory. These are usually artifacts of the revision control system
used by the Debian maintainer and not useful in a diff or native package.
dpkg-source will automatically exclude these if it is passed
-i for native and non-native packages respectively.
Refer to the dpkg-source(1) manual page for details.