A LONG LOST CARD MARKING SYSTEM 

Described is a playing card marking system formed on a deck of playing cards. The deck of playing cards includes a plurality of playing cards. While the front side of each playing card depicts a value and suit, the back side of each playing card includes a pattern having one or more markings therein. The one or more markings represent both the value and suit of the playing card and are formed near an edge of the playing card such that when the deck of playing cards is beveled, the one or more markings are visible. Thus, using the deck of playing cards a magician can easily identify both the value and suit of any given card within the deck.

https://patents.google.com/patent/US20180154245A1/en?q=mentalism+magic&oq=mentalism+magic