Unless you are willing to escalate the issue and deal with all the hassles associated with such action, of which there will be plenty, yes they can. Like someone else said, what are you going to do about it? I gaurantee you arguing with a NYC cop about such a thing in public is only going to end up in a physical confrontation with you likely to get your head knuckled. You think zero tolerance is just at public schools, try taking your knife back from a uniformed cop at a subway stop in Manhattan. I gaurantee you a bad day then.