In the old documents, we often see the economical writing style with the elliptical mark “_??_”. The basic usage since the Zhou dynasty of the mark is to show that the character followed by the mark should be read twice: ‘A_??_’means ‘AA’. And from it, another usage developed in the dictionaries of the Tang dynasty: the same character in annotations at the head one is replaced by “_??_”. The aim of this paper is to give some examples and to observe several phases of the usages of “_??_”.