It should be the D.S. mark, which derives its meaning from the repetition of the mark.

D.S. is the abbreviation of the Italian "dal segno", which means repeat from the mark and is a musical repeat mark.

Music repeat notation is a recording form that omits methods in order to save space in music scores and facilitate the writing of music scores. It is mainly divided into D.C. marks, D.S. marks, paragraph repetition marks, repeated skip marks and repeated omission marks.

Extended information:

The D.C. notation is the abbreviation of the Italian "da capo", which means repeat from the beginning. But when the Fine mark appears, it repeats until the Fine mark ends.

The symbol for paragraph repetition is the colon before the termination line. If there is a terminal line before and there is a colon after the terminal line, it means repeating the section between the two repeat marks; if there is no repeat mark before, it will repeat from the beginning.

The repeated skip mark is a supplement to the paragraph repeat mark. There are usually two paragraphs 1 and 2 or even more. It means that when playing from the beginning to the end of 1, then skip 1 and 2 from the beginning, and then end. .

The writing method of repeatedly omitting marks is similar to that of a sight. It means that when repeating, the part between the two marks is omitted and not played (or not sung).

Baidu Encyclopedia-Music Repeat Marks