What does a sharp sign indicate when used in representing a pitch?

Answer 1

In modern notation, the sharp sign (#) indicates that the note it precedes is sounded one half-tone (semitone) higher than without the sharp sign. In cases where the sign is applied to a note which is sharped in the key signature, it only indicates that the note should be played one semitone higher than if there had been no sharp in the key signature. To make an already-sharped note sharper by another semitone, the doublesharp (which looks like an ornate x made of angled diamonds) is used. To make an already-sharped or double-sharped note sound it's natural pitch, a natural sign (which looks like a square with lines rising from the upper-left and falling from the lower-right corners) is used.

Also, it is good to know that, in modern notation, accidentals (sharp, flat or natural signs applied in-line with music rather than at the beginning of each line or the beginning of the piece) continue to affect the note to the end of the measure. So |#C D E C| D E C E |is played #C D E #C D E C E.

In original-notation, preceding the 19th Century (up to the middle-end of the Baroque period), a sharp could be used to cancel a flat (and vice versa), and the sign we now call natural was used (esp. Germany) for the "hard B", i.e., what we now call B-natural. An accidental applied to a note often only pertained to that note in that octave, which is why a key signature for G major (in which F is sharped all the time, unless modified by an accidental) the key signature has two sharps for a treble-clef staff, one at the top line and one at the bottom space. This is only useful information if you are a) a hopeless trivia buff or b) actually trying to read original manuscripts or prints.