First,we can assume that rod's charge before the contract is Q,and after the contract,because the pith ball is electric neutrally,the Q electric quantity would balanced divide,both rod and pith ball would obtain 1/2Q electric quantity.So the rod's charge before and after the contact had the same sign.
In this question,the essence is the pith ball is neutral,so there is not added charged in this system.Therefore,the sign of the charge would not change.