You came to right place!
Here we go:
You can carry a knife, if the blade is 4" or less. If you carry a knife larger than that, and it is seen or found on your for any reason, you will be charged with a criminal charge of posession of a knife over 4". A violation of New York City Administrative Code.
Now...rule #2. Even if you have a"legal" knife you are carrying, you must acrry it concelaed. If it is visible in any manner, such as the pocket clip on your jean pocket, you can be charged with carrying a knife in public view, another criminal charge violating the NYC Administrative codes.
If you have ID, in most cases, (and the knife is not huge or unreasonable), you will be given a summonses for each and told to move on. You may or may not have the knife taken if it is over 4". Officer discretition. The summonses will give you a criminal record when you go to court.
Do cops enfocre it? Yes. These summonses are a "hot-topic" right now. It is being enforced. So they see the clip...they will come up...ask you for ID..tell you where to keep your hands...remove the knife...check its size and issue you 1 or 2 summonses as appropiate. Just put it in your pocket...completely. If you have it out, and not doing something with it, you could be charged with menacing and criminal posession of a weapon.
-In God we trust. All others, put your hands on the car and don't move.