The final shot of the series is of the outside of the manor where the Triquetra symbol of the Power of Three flashes onto the screen before cutting to the credits.
The original cross, kept at the Canterbury Heritage Museum, is a bronze cruciform brooch, with triangular panels of silver, incised with a triquetra and inlaid with niello.
Michonne makes her first appearance near the end of the second season finale, "Beside the Dying Fire", wherein she saves Andrea from a walker by decapitating it with her katana (which features a triquetra on the inner crossguard.