I dont like this "sign" operand. We can get rid of it, thereby making the equation longer and therefore look more complex (which is really what we're after right?), by making it:
Ps = Q/T * (1 + (-1^(ceiling(S/Q))(1 + ln|(S-Q)/Q|)

This change works as long as S > 0, and if S = 0 then stop doing math and yell "rebuy" as loud as you can.