Internally, an ECMA compliant interpreter must be able to distinguish between +0 and -0 although from a mathematical standpoint the values are identical. Where calculations involve the likelihood of +infinity and -infinity, the sign can affect the outcome, and so can the sign of the zero value. For example the reciprocal of a very small number.
We have quietly ignored the sign of a zero value where it would make no difference. There are some discussions where it becomes important and so the sign is retained here for illustrative purposes.