What is marked playing cards? Keep it quiet. However, it is true that some magicians and mentalists use marked decks. A marked deck refers to a deck with secret marks at the back of the cards that allows you to identify the value or suit on the other side by simply looking at the card back. How does an marked deck work? There’s two main types you’ll see in commercial production of marked decks: reader systems or coded system. Marked decks that use reader software look exactly like you would expect. The card information is hidden somewhere in the back of the deck. 7S would be 7 of S…