I carry a Gerber 400. Less than 3 inches, locks, does not look threatening. Very thin profile will not attract attention. So inexpensive that you will not care in the unlikely event it is confiscated.
Realistically, in NYC if you go into the wrong neighborhood no knife will help against 5 or more armed gang members. If you are accosted by someone who came looking for trouble, they have artillery. You only need a knife as a tool. I am 56, I hung on the streets as a youth, worked with the NYC Marshal seizing vehicles with delinquent traffic violations. That meant the worst neighborhoods in the middle of the night taking peoples rides. I have never been without a blade, but I have never pulled one out as a weapon.
Carry a 4 D cell Mag-Light. You don't have to hide it, it will not get you in trouble, you can keep it where you can deploy it faster than a knife, it has the reach of a bayonet and if defending against someone who is armed with a "weapon" they are clearly the villain, you are clearly the victim. And Damn, they hit like a Louisville slugger!