The reform movement based at Cluny in France was probably the most significant monastic movement of the tenth and eleventh centuries. While a monk there, Udalric composed a book called The Ancient Customs of the Monastery of Cluny (circa 1086). Among many other topics, Udalric describes the sign language used by monks when they were not allowed to speak.

For the sign for bread, make a circle with both thumbs and index fingers, since bread is usually round. . . .
For the sign for beans, place the tip of the index finger on top of the first joint of the thumb, and in this way make the thumb stick out. . . .
For a general sign for fish, imitate the motion of the fish's tail in the water with your hand.
For the sign for honey, stick out your tongue just a bit, and apply...