All reports of orig-tarball-missing-upstream-signature for the archive. The extended description of this tag is:
The packaging includes an upstream signing key but the corresponding .asc signature for one or more source tarballs are not included in your .changes file.
Please ensure a <package>_<version>.orig.tar.<ext>.asc file exists in the same directory as your <package>_<version>.orig.tar.<ext> tarball prior to dpkg-source --build being called.
If you are repackaging your source tarballs for Debian Free Software Guidelines compliance reasons, ensure that your package version includes dfsg or similar.
Support for signatures was added to pristine-tar in version 1.41 and support in git-buildpackage is being tracked in #872864.
This tag has not been emitted in any package tested by Lintian.