sign conventions in relative motion when objects travels opposite direction

@ ajay 
there are two sign convention which are generally used to follow the rule of relative motion . 
all the upward quantity are taken as +ve and all the downward quantity are taken as -ve . in this convention g in upward direction will be taken as -ve and the downward direction will be +ve . 
so, acc to your ques when object travels opp to the direction it will be -ve . 
but u need to choose frame of reference as correct . 

HOPE IT CLEARS ..