Virtue Guard
From UO: Origins - Wiki
Order/Chaos was not a part of the guild system in this era. Instead, only Great Lords were able to join the ranks of a virtue guard. Once you are a Great Lord, either approach an order guard at Lord British's Castle or a chaos guard at Lord Blackthorn's Castle and say 'virtue guard'. You will then receive the appropriate shield.
Although they will appear blue, Order and Chaos can freely attack each other as long as their shield is equipped. This includes inside of a guarded zone. You will receive no penalty for killing each other. Another useful thing about order and chaos shields is that you can cast a spell while having one equipped. This makes parrying a good skill for an order or chaos guard.