The audience will laugh when understanding the gag. The magician then repeats the effect with another spectator but asking him to sign the back of the card with the 52 printed cards.
This time, however, he will turn the back up of the chosen card among all the others shown on the prediction, which will not only have the signature of the spectator but can also be checked and left as a souvenir.
It's not only a gag, It's a funny routine!
You receive 25 “prediction” cards on which their faces are shown all 52 cards of the deck: 12 cards have the five of clubs turned with back up; 12 cards have the ten of hearts turned with back up; 1 card is normal (all the 52 cards are face up).