Текст лицензии: https://creativecommons.org/publicdomain/mark/1.0/
Я добавлю её, но имейте в виду:
The SPDX Legal Team considered this request during the September 10, 2020 meeting. At this time the request to add the CC Public Domain Mark is denied, but may be reconsidered at a different time. A good explanation of the standards for such a request can be found at https://wiki.spdx.org/view/Legal_Team/Decisions.Dealing_with_Public_Domain_within_SPDX_Files_(DRAFT) . The Public Domain Mark is not a license, but appears to be a legal conclusion that may be drawn by a reviewer much like an SPDX document.
Стоп. А чего вы предлагаете добавлять т.к. никакого legal текста не предоставлено по указанной ?