The two key signals that I learned were these:



One of my breakfast companions stepped away from the table for a bit but left his cutlery in the first position. When the server came by to pick up dirty dishes, I didn't let them take the dish because the silverware was in the "I'm still going to finish this; I'm just taking a break" position. That lead to a whole conversation where it became clear that no one else at the table had ever learned these signals.