The sign in such cases (i.e when one or both operands are negative) is implementation-defined. The spec says in ยง5.6/4 (C++03),
The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined; otherwise (a/b)*b + a%b is equal to a. If both operands are nonnegative then the remainder is nonnegative; if not, the sign of the remainder is implementation-defined.
That is all the language has to say, as far as C++03 is concerned.