A key signature consists of one or more sharps or flats written after the treble clef, or in the case of the key of C major, no sharps or flats. Because the G major scale contains the note F#, the key signature for the key of G major will consist of an F# note written after the clef.
This is the key signature for the key of G major. It has one sharp sign after the treble clef.
The C major scale contains no sharps or flats, therefore the key of C major contains no sharps or flats.
When a key signature contains sharps or flats, there is no need to place sharp or flat signs before individual notes. All the notes indicated by the key signature are sung as sharps or flats throughout the song.
It is possible to sing or play any melody in more than one key. You have just learned this song in the key of C major. Here it is again in the key of G major, which means that all F notes are now F#. Changing the key of a piece of music is called transposing. This process will be discussed in detail in Lesson 14.