The history behind the design
Arm yourself with knowledge. That's the only arming this t-shirt is about. It points you to the 63 clauses of Magna Carta 1215.
Arm Yourself is a call to arm yourself with knowledge. The 1215 Magna Carta has 63 clauses, and most of them deal with very practical matters: fair fines, inheritance, weights and measures, and the limits of royal officials.
Only three clauses of the 1297 version are still law in England and Wales today. They protect the freedom of the English Church, the ancient liberties of the City of London and other towns, and the right to justice and lawful judgement (the old Clauses 39 and 40). Knowing which parts still stand, and why, is the point of the design.