Wiktionary
note verbale
n. An unsigned diplomatic note written in the third person, of the nature of a memorandum but sometimes considered to be more formal.
Wikipedia
Note verbale
Note verbale (, verbal note) is a diplomatic communication prepared in the third person and unsigned: less formal than a note (also called a letter of protest) but more formal than an aide-mémoire. A note verbale can also be referred to as a third person note (TPN).