I would prefer another option NOT in the poll (and thus have not voted): Treat it as just another license statement. There are multiple ways this kind of “uncopyrightable” assertion is made, and I think that specific form should be captured as a license statement.

New entries should be created for at least the “CC Public Domain Mark” and the situation where someone in the US government does it as part of official duties & doesn’t claim a copyright. There’s a discussion going on here:
https://github.com/spdx/license-list-XML/issues/988

Treating it like “everything else” means there are no special cases for SPDX, *and* you get finer-grained information.

For those who object & say that “there is no license”, well, “license” is just synonym for “permission”, and in this case the permission is granted by the way the legal systems work. So it’s a permission granted by the underlying mechanisms of law ☺. I think the *users* of SPDX will appreciate the simplicity of *not* needing another special case.