These Ruling(s) have not been confirmed as applicable to the TCG.[Notes 1]
In place of declaring a FULL card name, a precise description of a card's stats, appearance, and/or effects, is considered acceptable so long as both players are in clear agreement over which card is being described.
Previously Official Rulings
These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: 
You can't activate "D.D. Designator" when your opponent has no cards in his hand.
If you activate "D.D. Designator" and your opponent has 2 copies of the same card in hand, you (the player who activated "D.D. Designator") select which of the 2 cards is removed from play (this can be important if your opponent holds your card because of "Exchange").
↑Konami Judge Program Rulings are considered unverified, as their source(s) are not publicly viewable. They are not confirmed as applicable to the TCG until they have been officially published by Konami.