In NY, it is requires that the knife lock open to be a gravity knife, and butterfly knives have been found not to be gravity knives due to the fact they do not lock open automatically ( about 6 case law opinions on this). That cleared up, the courts have held that butterfly knives are designed as weapons and are therefore "dangerous knives" and the same charge then applies. A knife that can be flicked open that does not lock can still be classified as a dangerous knife. The sad thing is that once an officer has decided to charge you with a weapons charge for any knife, the ADA 99% of the time goes forword with the charge. The judge will not see the actual knife at any one of the first two or three hearings, so the judgement of the officer will take you this far into the system once that ADA allows the case to proceed. The safest knife to carry in NYC would be a non locking SAK or slip joint. A locking knife should have a very tight blade that can not be flicked open ( even holding the blade and flicking the handle), and not have a blade that is designed as a weapon ( tanto, spear, bayonet, kriss, dagger, double edged). Never ever say you are carrying any knife or other item as a weapon! A roll of quarters carried as a weapon to use in punching, can get you the same charge as a dangerous knife. If you state it is a weapon, you show intent under NYS law. Many officers will lead you down the path during questioning, asking why you are carrying the item. Your "rights" do not need to explained to you until the officer believes he is obtaining evidence leading towards a arrest or that a crime has been committed and the officer is investiagting a crime. If an officer ask you why you have a items under normal conversation, and you offer that it is a weapon for SD, then you have given him enough information to charge you that will ( and has ) held up in court.