Signature is a supertype that may apply to game objects of any card type. It impacts the rules for deckbuilding. See rule 103.2.d. for more information about Signature cards.
§ 133.7.b Core Rules PDF (officieel)
§ 133 Category
§ 133.7 Supertypes are Categories that may apply to game objects of multiple types. They are listed before a card’s type.
