The silent service code is a way for a diner to "talk" to servers during a meal without saying a word, mainly to tell them that the diner is finished. This will prevent any embarrassing situations where the server would take a meal prematurely.

To tell a server you have finished place your napkin

Napkin

A napkin, or face towel is a rectangle of cloth used at the table for wiping the mouth while eating. It is usually small and folded...

 to the left of your plate

Plate (dishware)

A plate is a broad, concave, but mainly flat vessel on which food can be served. A plate can also be used for ceremonial or decorative purposes.-Materials:...

, and place all your utensils together in a "4-o'clock" position on your plate.

Utensils crossed on a plate signify that a diner is still eating.

If you must leave during the meal, you should place the napkin on your chair to avoid any confusion.

The code is almost always taught during business dining etiquette

Etiquette

Etiquette is a code of behavior that delineates expectations for social behavior according to contemporary conventional norms within a society, social class, or group...

classes.