Another one is illegals signing a voter registration form. States almost never prosecute. It is voter fraud and criminal offense to knowingly register a person or person to falsely register to vote.
States like CA figure the affadavit statement "under penalty of perjury" is sufficient proof of US citizenship.
CA Elec Code § 2111 (2017)
A person may prove he or she is a citizen by his or her certification under penalty of perjury on the affidavit of registration.
CA Elec Code § 2112 (2017)
Notwithstanding any other provision of law to the contrary, the fact that a person certifies to his or her United States citizenship by signing his or her affidavit of registration shall be deemed evidence of citizenship for voting purposes only.
https://law.onecle.com/california/elections/2111.html