It's common to see whiskey jugs in cartoons regarding Appalachian culture portrayed with three X's.

According to modern folklore, the X marking indicated how many times that particular batch of moonshine was distilled.  Three X’s meant that the moonshine had been run through the still three times, making it the closest you could get to pure alcohol.  "XXX" = the really good stuff.

This was done before modern distilling techniques, and quickly implied the meaning in cartoons and illustrations.