The red cross on the knight's shield and surcoat is usually associated with the Knights Templar, a medieval Christian military order. It symbolizes their dedication to the Christian faith and their role in the Crusades.

It can mean a kilt, a child's smock, surcoat, petticoat. A south Wales variant.

Into battle they wore a shirt and hose. Over that they would have worn a gambason, a type of padded shirt to cushion blows. Over that they would have worn chain mail to deflect glancing sword strikes. Finally a Surcoat would be worn over everything else. The Surcoat displayed the knight's identifying mark or icon on the battlefield and also it protected the mail shirt from mud and water as with all metal forms of wear it was prone to rust.

No, a seal is a device used for making an impression in wax or other soft material to authenticate documents, while a coat of arms is a unique heraldic design on a shield or escutcheon or on a surcoat or tabard used to cover and protect armor and to identify the wearer.