The two hash marks on the staff represent the sharp sign.

In the staff notation, there is the meaning of "sharp half tone", which is usually called "sharp sign" and is written on the left side of the note head. Or it can be written at the beginning of the entire line, which means that all the specified notes in the entire line are "raised by a half step", which means that the original note is raised to the key above it.

The sharp mark is a mark placed on the music line or the gap between the music lines#

The sharp sign is used to indicate that the pitch is half a degree higher than without this mark.

Extended information:

History of staffs

In the early Middle Ages in the West, people used neumes to record music scores. Newm notation uses horizontal lines as the standard. It can only express the pitch through symbols, but it cannot accurately express the length of the note value. At that time music could only be recorded through these mnemonics.

From the 9th to the 11th century, many musical notations made extensive use of more precise note spacing, using nuum symbols to represent absolute pitches on the page, such as the Italian Longobardian and Beneventan nuum notation manuscripts of 1000, which are A short Numu notation manuscript made using a method similar to the combination of modern phonetic letters and Numu symbols. Additionally, many early musical notation manuscripts use one or more parallel lines, indicating specific pitches.

Modern staff notation originated from Gregorian chants around the 12th century. At that time, pitches were mainly represented by words combined with symbols. However, some people began to try to record Gregorian chants with lines at that time.

And over time it progresses from starting with just one line to four lines, using only dots to represent notes. At that time, because the tonality and range of musical instruments were different, there was no standard for how many lines a score should be used for.

The earliest existing parchment music score was made in 1342 and contains 4 lines and 3 spaces. The music score of 5 lines and 4 spaces was made by Italian Ugolino of Forlì. It can be seen from the Italian pentagramma of the musical score that the musical score has 5 lines. In the 16th century, France took the lead in integrating their music into a staff system, which soon became widely spread in Europe.

Baidu Encyclopedia - Staff