I often think it would be cool if there was a widely understood hand sign for asking people in a restaurant how they rate it. You stand outside the window and make the "Is it good?" sign, and whoever sees it from inside would hold up 1 to 5 fingers to give their star rating.

Point twice to them. Point to the space in front of your lap. Point to your face and mimic sad face and later happy face, while pointing your thumb down then up, à la Roman emperor.