You might wear a special ring to secretly mark the cards while you’re playing.
"Card sharping has been reduced to a science… It is no longer a haphazard affair, involving merely primitive manipulations, but it has developed into a profession in which there is as much to learn as in most occupations."
-John Nevil Maskelyne in Sharps and Flats, 1894
Here are two longer articles, one from Invention and Technology Magazine and the other from Cabinet, that reveal the various methods card cheats use to mark cards.
Before decks of cards had back designs, card sharps could use natural imperfections to tell the cards apart, but once back designs began to be printed in the 1850s, the cheats developed and refined their methods, using such means as inking, daubing, dying, smudging, pin pricking, scratching, dulling, juicing, glossing, waxing, sunning, ironing or glazing the cards. Some of these methods are practically undetectable, and combined with other concealed technologies and deceptive sleights, a card cheat has an undeniable advantage.
– The Science of Cheating At Cards – The centuries-old battle between swindlers and their prey has produced a small universe of technologies, American Heritage, Invention and Technology Magazine>>
– Mark of Integrity, Cabinet Magazine>>
– Sharps and Flats – a complete revelation of the secrets of cheating at games of chance and skill (1894) – John Nevil Maskelyne>>
See also this Deceptology post about one of the card shark’s technologies: They stole almost $900,000 from a casino using 19th Century technology>>