The widely-known symbol of the Courts is the triquetra. [Will add picture.] Mages of the Courts are expected and technically required to wear a triquetra pendant to display their affiliation, but some choose not to. Traditionally, the Low Courts make their pendants of bronze, the Middle Courts of silver and the High Courts of gold, but this has been fudged over time. With almost no exception, the pendants have the stone of (the color of) the mage's court in the middle.
The history of the Courts currently resides in the depths of Marvin, and I'm not there. But, the Courts date back to the 16th century, having changed only in nature over time - what organization and traditions were then established still prevail, while the goals and means of the Courts may have changed.