A signature is presumed to be genuine and authorized if it purports to be the signature, affixed in his official capacity, of an officer, or deputy of an officer, of a nation or public entity in a nation recognized by the executive power of the United States and the writing to which the signature is affixed is accompanied by a final statement certifying the genuineness of the signature and the official position of (a) the person who executed the writing or (b) any foreign official who has certified either the genuineness of the signature and official position of the person executing the writing or the genuineness of the signature and official position of another foreign official who has executed a similar cetificate in a chain of such certificates beginning with a certificate of the genuineness of the signature and official position of the person executing the writing. The final statement may be made only by a secretary of an embassy or legation, consul general, consul, vice consul, consular agent, or other officer in the foreign service of the United States stationed in the nation, authenticated by the seal of his office.