Possible Clues:

• Key of Bach's second violin concerto: Abbr.
• Mus. key with four sharps
• Key of the last movement of Mendelssohn's Op. 64 violin concerto
• Key of Vivaldi's "Spring Concerto": Abbr
• Key of Haydn's Symphony No. 12 or 29
• Key of Haydn's Symphony No. 29
• Key of Beethoven's 'Fidelio' Overture: Abbr
• Key with four sharps, for short
• Four-sharp key: Abbr
• Key of Dvorak's 'Serenade for Strings': Abbr