The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
The file is setuid or setgid and has a mode different from any of 2755, 4755, 4754, or 6755. Any other permissions on setuid executables is probably a bug. In particular, removing root write privileges serves no purpose, group-writable setuid or setgid executables are probably bad ideas, and setgid executables that are not world-executable serve little purpose.
Refer to Debian Policy Manual section 10.9 for details.