As a freshman theory student I was required to name all the keys signatures within a minute as my professor listened with stopwatch in hand: 1 sharp G, 2 sharps D, 3 sharps A, etc. It’s important to know them, and its also good to take moment to look at the key signature as preparation for playing.
Determining the Key with Flats in the Key Signature
Determining the Key with Sharps in the Key Signature
