If the applicant is a naturalized citizen, or if the applicant has acquired citizenship by reason of being born abroad to a United States citizen parent or has derived citizenship through the naturalization of a parent or spouse, the certificate of his naturalization, under the seal of the court issuing the same, or a copy thereof issued by the United States Immigration and Naturalization Service in lieu of the original certificate, or a certificate of citizenship issued by the United States Immigration and Naturalization Service, or a passport issued by the State Department of the United States on or after January 1, 1948, or a written statement signed by a town clerk or registrar of voters of a town of this state or by an election official of another state in the United States or a town or political subdivision of such state that the records of such state, town or political subdivision show that such applicant has previously been admitted as an elector therein, shall be conclusive proof of citizenship. Any applicant submitting documentary evidence of citizenship shall make oath that he is the person named therein.