Every membership is a physical object with a verifiable history. The card opens the door, proves standing at the bar, and carries the sponsorship chain that produced it.
A printed QR code is not authentication. It can be photographed, reprinted, and presented by anyone — which makes it fine for a table menu and useless for a door. The Mark uses a secure NFC chip embedded in the card that generates a rotating cryptographic code on every read, verified server-side against the club's own key. A code that has already been used is dead. A photograph of the card proves nothing.
What it does not do: it does not replace a person at the door, it does not make a card impossible to lose, and it does not authenticate a member who hands their card to someone else. It makes a forged card impractical and a shared card traceable, which is the honest version of the claim.
The same chip and the same verification path run the bottle-locker sign-out and the guest register, so one credential covers the door, the bar, and the book.