I am writing part of a piano piece in a hexatonic "key" containing these notes:
C - D# - E - G - Ab - B
(I say "key" instead of scale because I'm treating it like a key, deriving not just melody but also the chords from this "key", and staying mostly "in key". If you think that this is not a key but a scale, feel free to call it a scale in your answer.)
The "key" is the same when transposed up or down a major third, but it makes most sense to see this part as being in some sort of key of C, because it starts with a C minor-ish feel and ends with a C major-ish feel.
Now I'm wondering how to notate this. Do I consider the D# and E to be an Eb and Fb in order to have a key signature with only flats? Or would three flats just confuse people into thinking the part is in Eb? Do I use a novel key signature with a sharp and a flat? Or should I notate this in C and use accidentals for D# and Ab? Maybe there is a precedent?