Focus on caller
The partner who will be responding to a call, should keep their eyes and focus on the partner who is calling. A common mistake is for the partner who is responding to a call to ball watch. By focusing on the ball, the batsman will lose those visual cues whether the other partner will run or not.
Whilst running and deciding upon returning for another, mid pitch the batsmen can communicate whose call it is. The other partner should then focus their attention on the caller.