Q: building on the question someone else asked, how can you really differentiate, say, A# minor from Bb minor?
A: they sound the same, but on paper they look different. on paper, the key of Bb minor will have a lot of flats in the key signature. the key of A# minor will have a lot of sharps in the key signature. and in A# minor, all the note heads will be written slightly lower on the page