The effect's an oldie: a deck is displayed face down as normal, it's turned face up and a card is removed from the spread.
The deck is pocketed while the performer explains that he had a flash of intuition earlier and marked the back of one card with an X. The selected card is then turned face down, and it is seen to have an X on its back.
It's accomplished by having half the deck (the bottom half) X-ed on their backs. The face-down display only shows the top (unmarked) half; the face-up spread for selection only spreads the bottom (X-ed) half.
Okay, card guys. Who came up with this first, and where is it published?
Thanks for your help!