During American Slavery, slaves were not allowed to learn to read.

Many liquids were kept in jugs.  Some liquids were drinkable, and some liquids were poisonous.

To prevent kids from accidentally drinking poisonous liquids; potters created ugly jugs.

Ugly jugs held poisonous liquids such as gasoline, kerosene, and ethyl alcohol.

The jugs with faces were made extra ugly and scary to prevent children from drinking from them.