A deck is removed from it's case & shuffled.  Anyone is asked to name any card in the deck. 

That card is removed from the deck and a colored sticker is affixed to it's face for identification.  The card is returned to the pack. 

When the deck is turned face-down & spread out ONE CARD is found to have a different colored back and you've guessed it.....IT"S THE CHOSEN CARD complete with the sticker on it's face!!!