Possible Clues:

• Oblong
• Maybe square uniform sandwiches can't burst
• Like some figures normal around copper's first beat?
• First sign of Charlie Brown in uniform — as form of comic strip?
• Of a right-angled parallelogram
• Soldier carrying cape, brown, as a flag, for example
• A four-shaped, perhaps
• A central rug moved to be at ninety degrees
• Regal cat run (anag) - right-angled