What is the sign of c : d when c > 0 and d < 0

When the number of negative signs is odd in any expression involving multiplication and/or division, the result will be negative.

When the number of negative signs is even, the result is positive.

You can check the sign by replacing each factor by + 1 if it is positive and - 1 if it is negative. Your problem has + 1/-1 = - 1. The sign of the result is negative.

negative

positive/negative = negative