Recall the following properties of multiplication of signed numbers:
(positive)(positive) = positive
(positive)(negative) = negative
(negative)(negative) = positive
When more than two numbers are being multiplied, just count the number of minus signs:
any even number of minus signs collapses to a plus sign;
any odd number of minus signs collapses to a minus sign.
Input your answer as: $\quad+\quad$ or $\quad-$