The tag is present in Lintian version 2.104.234. That is the most recent version we know about.
The user or group ID of the owner of the file is invalid. The owner user and group IDs must be in the set of globally allocated IDs, because other IDs are dynamically allocated and might be used for varying purposes on different systems, or are reserved. The set of the allowed, globally allocated IDs consists of the ranges 0-99, 64000-64999 and 65534.
It's possible for a Policy-compliant package to trigger this tag if the user is created in the preinst maintainer script, but this is a very rare case and doesn't appear to be necessary.
Refer to Debian Policy Manual section 9.2 for details.