From the first chapter of The Devil's Cloth : A History of Stripes:
In the medieval Western world, there are a great number of individuals — real or imaginary — whom society, literature, and iconography endow with striped clothing. In one way or another, they are all outcasts or reprobates, from the Jew and the heretic to the clown and the juggler, and including not only the leper, the hangman, and the prostitute but also the disloyal knight of the Round Table, the madman of the Book of Psalms, and the character of Judas. They all disturb or pervert the established order; they all have more or less to do with the devil.
In the Middle Ages, Fortune, who turns the wheel of destiny for man, often wears a striped robe. Today, on a playground, the schoolchildren in striped clothes always seem more active than the others.
Thanks to the frequent wearer of stripes, Rose Gowen.