What music sign that means to hold a note for its full value?

The music sign that means to hold a note for its full value is called a fermata. It is a symbol that looks like a small semicircle with a dot in the middle, and is placed above or below a note. When a fermata is placed above or below a note, it indicates that the note should be held for its full value, regardless of the tempo of the piece. This can be used to create a sense of emphasis, or to add a dramatic effect to a performance.