LOL.
Juice is a system that has problems with lighting, and is too expensive to bother looking into for something as small as this. D ICE R's idea on scratch marks with the nail is a suitable one, but that depends on what the card will be used for.
If this is one of those routines with a sucker card which the spectator has to get, try this. Use 3's and a King as the sucker card, and offer to let them look at and pick the first card of their own choice. Naturally, most will choose King.
If you want to still have it marked, you could also just try nail nicking all 4 edges of the card, but that might be hard to spot. You could also try crimping all the cards length-wise in a convex manner and the sucker card length-wise in a concave manner. That way, you should be able to see the difference when the light hits it if you're paying attention.