A Clash of Arms (Cycle) とKingsroad (Cycle) 以外での、Siege (Trait) を持つカードは１枚のみのようです。
(Unique) Tyrion's Chain
Type: Attachment / House: Lannister
Attach to a location. Kneel that location. If you lose a Military challenge, discard Tyrion's Chain from play. Response: After attached location is knelt, kneel all locations controlled by the attached location's controller.