The spectator can check the corner to confirm that it matches their card.
For your consideration:
1) No gimmicks
2) So visual and direct
3) Everything is examinable
4) The spectator can hold the box and can keep it after the effect
5) You can also do it with bills
6) Easy to do
7) Quick reset
It is a great visual piece of magic you can do without any gimmicks. So check this out.