There are twelve different scales in music. Each scale has its own key signature. Here are the major scales that use sharps #. G major has one sharp, D major has two sharps and so on.
Here are some examples of key signatures that use flats b. F major has one flat, Bb major has two flats, Eb major has three flats and Ab major has four flats.
The scales that use sharps # are G, D, A, E, B and F# major. The scales that use flats b are F, Bb, Eb, Ab and Db major. The scale of C major does not have flats or sharps as it does not contain any sharps or flats in the scale.
An easy way to remember if the scale has sharps or flats is; if the scale has sharp in the name such as F#, it will contain sharps. If the scale has flat in the name such as Bb, it will contain flats. If the scale does not contain flat or sharp in the name such as A major or B major, it will contain sharps. The exception to the rule is F major which has one flat, so we need to remember this one.
So examples are: remember F major, one flat and C major, no sharps or flats.
A major-sharps, F# major-sharps and Bb major-flats, Eb major-flats.
Warburton, Annie O. Basic Music Knowledge. Cambridge: Cambridge University Press, 1995. Print, p. 32.