One-way deck

A one-way deck is a deck of playing cards where the back of the cards has a pattern which 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 can also be used as "pointer cards" (the Seven of Hearts, for instance, whose odd heart image can point in one direction or another) which, when all aligned, allows an otherwise ordinary deck (one where the backs are all identical) to be used as a partial one-way deck.

In fact all sevens may be used in this manner because of the placement of the seventh marking, which is always on one side or the other of the median line. No other card can reliably be used in this manner although in many decks various clubs, hearts and spades can be used since these are different when turned over.