Thalians

When the Constraints were written, it was agreed that magic users over a certain level must be trained, in order to avoid large accidents and to hopefully instill ethics into the most powerful. The Tower of Rust and its mage training already existed and the head of it agreed with King Willark I and the Constraints. In order to prove that a mage had the appropriate training, the custom of Thalians was created. 
Each mage receives a disk or badge from their teacher, when the teacher feels that the student's training is sufficient for them to go out on their own. The badge has a symbol of the teacher on one side and the symbol or name of the student on the other. The badge is usually made of metal and has been charmed so that the badge is tamper proof. The badge usually has a small hole at the top and at the bottom, so that someone who has had multiple teachers can connect their badges. If a lineage derives from a particularly strong or famous mage, the entire lineage from master to student may be strung together. This badge or chain of badges is known as a mage's thalian. When a mage is questioned by the Royal or Provincial Guard, the thalian is their proof that they have done the required studies and, theoretically, are not a threat to a community due to an inability to control their magic.