more of a stage effect, if it helps any.

I don't know if this was mentioned yet but John Kennedy has a card stab with a swiss army knife appropriately titled "Mid-air Card Stab".

Bill Abbot has a routine, the name escapes me at the moment, that is similar but more suited for walk-around type environments, such as restaurants, but the cards are placed in a brown lunch bag the spectator shakes it up, you stab the bag, and their card is on the knife. This is one of my favorite effects to perform, plays huge.

I live in Ny one of the most strict places in the country when it comes to owning a weapon and anyone above the age of 16 is allowed to carry a knife anywhere below 4 inches , so i figure he should be fine, also it is not brandishing a weapon if it is used in the course of work requiring its use ( such as a cop with a gun or a construction worker with a knife) or in the midst of a performance I actually had to look this up when I was trying to start a busking routine, although this is one states rules, Im sure there are similar laws in most states, also, with the excuse of it being for magic, and plenty of witnesses saying this is what you used it for I'm plenty sure you would get released on your own recognizance if you even got picked up in the first place ( which i have, for crimes unrelated to the act of magic )
If you lie anywhere outside of the US ( the uk for example a place with a very very low tolerance for any weapons) this may not apply