This is a classic magic trick as old as this hills isn't it? You sort a deck of cards so that the backs are all oriented one way (the pattern on the back is usually not exactly in the centre), and then you rotate the chosen card 180 degrees so you can relocate it even after shuffling.
I don't know the name of the trick but I learnt it as a child.
I don't know the name of the trick but I learnt it as a child.