Why is the key signature completely different from the actual notes?

Question

Beginner here. So, I wanted to play this little phrase that is written, supposedly, in A major with 3 sharps on F, C and G. However, every G has a natural sign and there's a B and a E with sharps (no C or F by themselves), practically making it a C major. Why does it have to be so hard to read when it can just be written with natural notes?

Similar questions have been answered again regarding classical pieces and the evolution of scales, but this is a 2016 hip hop song. Does it have anything to do with alto saxophone being tuned in Eb?

Answer 1

That seems just a poorly written arrangement, with wrong keys, chords, notes and transposition.

The song is indeed in F minor, so it should have 4 flats, and since the melody is written for Alto sax, that part should be written in D minor (one flat).

Also, the second bar should be Ab and the third Db.

The reason for that (wrong) transposition is that songs are often written without key signature for simplicity (especially if they use tonalities with few accidentals), but that can clearly become a problem for transposing instruments, and if you do want to write without key signature, that should be done for all parts.

In any case, even assuming the above, many of the notes in the second and third bar are completely wrong: B# and E# should obviously be C and F natural.