Crimp

This involves putting a bend or crease in a playing card in such a way that you are able to locate it in the deck by feel alone. The crimp can be put anywhere on the card, but the corners or long sides are generally used. You can crimp the card simply by bending the corner slightly upwards when showing it. You can also crimp the side of a card by squeezing it gently at the side between the thumb and forefinger. Basically, any (subtle) identifying bend or crease in a playing card qualifies as a crimp.