Invisible Ink Marked Cards
What are invisible ink marked cards? They are the playing cards that marked on the back with invisible ink. They are often used to cheat for casino gambling games or card tricks, and also can be used regardless of who shuffles and deals the cards.
However, how do people mark poker before this new technology shows up? Easily, poker players, especially magicians, would add some subtle visible marks or alter the color, pattern, etc. on the back of the playing cards. For example, adding unobtrusive hieroglyphics in white areas of the card is an excellent way. Of course, these changes are visible but minimal.