One-way deck
A one-way deck is a deck of playing cards where the back of the cards has a pattern that can be oriented to have a "top" and "bottom". Magicians and card sharps can use the orientations of cards in one-way decks to encode information that allows them to perform card tricks.
A certain number of the faces of playing cards are not symmetrical, and therefore can also be used as "pointer cards". When all aligned, these cards allow an otherwise ordinary deck to be used as a partial one-way deck.
