non-transposing key signatures
Non-tonal music is normally written with no key signature at all. Transposing instruments should not get one. Sibelius does this by allowing you to specify an "open" key signature - looks like the key of C, but doesn't tranpose. Finale does it by specifying "chromatic" as opposed to "key signature" transposition. I think Sibelius' implementation seems simpler but either works.