The A-Card
The Codex Belli introduced the concept of the A-Card (the "A" is for "Authorisation") or "driver's license for reenactment" as it has been nicknamed by supporters and critics alike. The A-Card is essentially a card qualifying the owner as a verified safe fighter listed at the Kämpferliste. This list is maintained by the same group that issued the Codex Belli and thus the A-Card is also intended to verify that its owner knows the ruleset and has proven to be able to fight without violating it.
The A-Card was deemed necessary when events grew too large to rely on individual reenactors' reputations as safe fighters or on-location safety tests.
However the A-Card was also strongly criticised for being less reliable, as the owner could become unsafe after acquiring the card (e.g. due to a lack of practice), which wouldn't be an issue in the case of on-location safety tests or an honour based system in which another person, usually the group leader, would assure that the combatant is safe and jeopardize both their and the combatant's honour if the combatant then proved unsafe.
In the past it has also been poked fun at for being too bureaucratic and not applicable in the Real World.
Many implementations of the Codex Belli ignore the A-Card and instead rely on safety tests or observation during warm-up.
Read more about this topic: Codex Belli