*sigh*
The law requires a blade length of less than 4 inches. However, there is also an anti-switchblade law on the books, which also prohibits gravity knives. The law enforcement in NYC has, however, decided to enforce a rather liberal interpretation of this law, classifying as a gravity knife any blade which "flicks" open under any application of force. This, of course, includes the flick of a wrist, or even the flick of an elbow.
There's also the question of intent - if a police officer decides that you seem to be possibly the type of person who might go and commit crimes with your gravity knife, then it doesn't matter what you're carrying. Tuck your shirt into your pants? Then you'd better forget that clip - if a cop sees that telltale bit of metal on the outside of your pants, good luck to you.
Friendly, eh? I'd suggest you tighten up whatever you carry. The Military is a definite no-no - it'd get you into the police station no matter how tight you've got that thing.
This is not based on my personal experience, thankfully - it's been the experience of one good friend and several acquaintances. The knife situation in NYC is well-known, and you should prepare yourself for the worst should you carry a conveniently carried, practical and easy-to-open knife in our fair city...
P.S. - If you decide to carry it anyway, don't open it in front of anyone whose reaction you can't gauge - NYC is a bastion for ultra-liberal types who'd scream for the cops if you so much as brandished a sharp piece of paper at them. Good Lord, I hate admitting that...