"Designator" (めいしゃ Shimeisha) is a series of Spell/Trap Cards that allow you to declare a specific trait of a card (often a card name) and apply various restrictive effects to that card.

"Appointer of the Red Lotus" is a part of this series because it has an appropriate effect, as well as it having the appropriate kanji for "Designator" in its Japanese name, despite its TCG translation.

Gishki Designators - Recommended Cards