All musical key signatures can be identified from the number of sharps or flats written in the heading of the stave music. Here's a mnemonic sentence denoting the order of entry of sharps in the signatures:

" Frederick Charles Goes Down And Ends Battle "
(F#, then C#, G#, D#, A#, E#, B#)

For key signatures requiring flats the order is reversed (Bf,Ef,Af,Df,Gf,Cf,Ff):

The sharps and flats are equivalent to the black notes on a piano. The key of C doesn't have any sharped or flatted notes in its scale, but the key of G has one (F# rather than F), the key of D has two (F# and C#) etc. Note that the order of keys rises in the same order as for sharps, ie. FCGDAEB:


Mnemonics Guide   Page 1997   An EUdesign site