autograph letter
英[ˈɔ:təˌgræf ˈletə]美[ˈɔtəˌɡræf ˈlɛtɚ]
In Vatican usage, an autograph letter is a letter signed by the Pope in which he refers to himself as "I", or using the majestic plural,?"we", as opposed to the more usual letter from the pope signed by a subordinate referring to the Pope as "he" and saying, for example, "The Holy Father has directed me to reply to your letter...".