Signature card - Yugipedia - Yu-Gi-Oh! wiki

A signature card is a card most associated with a Duelist, and tends to be used in a majority of their Duels. Duelists may have more than one signature card. They might have a connection and the Duelist may value it. Signature cards tend to be Monster Cards and to have alternate artworks in the OCG and TCG. In some cases, signature cards are created by their owners and/or only one copy of them exist in the anime like "Elemental Hero Neos" and the "Numbers".

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