In music notation you see keys denoted by sharps and flats.
Here is a fast and easy way to check on the sharps for a key.
Note five C chords in this manner:
CEG GBD DFA ACE EGB BDF# 
Key is the 5th, 4th is the sharp for that key: 
Key of G F#
Key of D F#C#
Key of A F#C#G#
Key of E F#C#G#D#
Key of B F#C#G#D#A#
      F# F#C#G#D#A#E#
Major Key(sharps++)= C,G,D,A,E,B,F#,C#(none,F,C,G,D,A,E,B)
Perhaps a better view with lines and spaces:
Note space/line
Treble amd Bass Lines Sharp Locations (Notes where # would appear)
KEY OF C   G   D   A   E   B   F   F#  C#
G    |   |   |   | G | G | G |   | G | G |
F----|   | F | F | F | F | F |   | F | F |
E    |   |   |   |   |   |   |   | E | E |
D----|   |   |   |   | D | D |   | D | D |
C    |   |   | C | C | C | C |   | C | C |
B----|   |   |   |   |   |   | b |   | B |
A    |   |   |   |   |   | A |   | A | A |
G----|   |   |   |   |   |   |   |   |   |
F    |   |   |   |   |   |   |   |   |   |
E----|   |   |   |   |   |   |   |   |   |
D    |   |   |   |   |   |   |   |   |   |
C----Middle C|   |   |   |   |   |   |   |
B    |   |   |   |   |   |   |   |   |   |
A----|   |   |   |   |   |   |   |   |   |
G    |   |   |   | G | G | G |   | G | G |
F----|   | F | F | F | F | F |   | F | F |
E    |   |   |   |   |   |   |   | E | E |
D----|   |   |   |   | D | D |   | D | D |
C    |   |   | C | C | C | C |   | C | C |
B----|   |   |   |   |   |   | b |   | B |
A    |   |   |   |   |   | A |   | A | A |
G----|   |   |   |   |   |   |   |   |   |
Key of C has no sharps, B has 5, Major Key(1 flat)= F(B)
minor Key(sharps++)= a,e,b,f#,c#,g#,d#,a#((-,F,C,G,D,A,E,B)

according we have:
KEYS: I ii  iii IV V  vi  vii   viii
      C Dm  Em  F  G  Am  Bdim  C
      D Em  F#m G  A  Bm  C#dim D
      G Am  Bm  C  D  Em  F#fim G
      A Bm  C#m D  E  F#m G#dim A
      E F#m G#m A  B  C#m D#dim E
      B C#m D#m E  F# G#m Amdim B
      F Gm  Am  Bb C  Dm  Edim  F

Major Key(flat++)= F,Bb,Eb,Ab,Db,Gb,Cb(B,E,A,D,G,C,F)
minor Key(flat++)= d,g, c, f, bb,eb,ab(B.E,A,D,G,C,F)

Rolling Stone songs have used 4#s,5#s,7#s,one#, and no 
sharpes (key of C) and 4 flats.
They would be in the key of E,B,C#/a#,G,C and Ab/f;
providing great riffs and the name Keef to the artist. 
Their guitars are in standard or open tunings and
have not seen tabs of half note detunings as Hendrix
would do on special songs. A trait of the virtuoso.
since Nicolo Paganini's E flat Major key Concerto no.1
was transcribed to D Major to clear the soloist from
re tuning problems.