This signature is believed to be ineligible for copyright and therefore in the public domain because it falls below the required level of originality for copyright protection both in the United States and in the source country (if different). In this case, the source country (e.g. the country of nationality of the signatory) is believed to be United States of America.
Note that this tag cannot be used on all signatures, as not all signatures are copyright-free.
This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 100 years or fewer.
You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.