Royal document measures approximately 14.0" x 8.5". "Her Imperial Highness, Empress Catherine III, " typed letter signed, dated 1965, to the Chinese Embassy.
Very bizarre letter, with stamps claiming she is the Legal Russian Government Taken Into Exile, 10 Nov. 1918, " and "Chief of Mission for The President of the United States, Lyndon Baines Johnson. At the bottom, there's a long statement about how she is the Legal Crown Ruler of The Romanov Dynasty through a secret coronation ceremony in 1942, and is also the Queen of Poland, Grand Duchess of Finland, etc.
Other example of Catherine III's signature can be found online, in the library collection of Davidson College.