At any given moment, no matter what time of day, there are roughly four million film productions taking place on the streets of Manhattan. And that's not including Law & Order. You can tell when you're getting close to one when hot dog carts subtly morph into trailers, or if they belong to A-listers, fortified land yachts.
Then you'll inevitably reach the Location Shoot's version of a bouncer: the obnoxious twentysomething Production Assistant, who will hold his hand up to you and stop you in your tracks without ever uttering a word or establishing eye contact. If you aren't immediately forced to backtrack and circle around, he will pretend to look important while using the walkie-talkie clipped to his belt until you are finally allowed to pass, indicated by another silent wave, this one accompanied with his eyes rolling.
Another problem you might encounter is the eye and neck strain you'll receive from attempting to see anyone famous while trying to look like you're too cool to care.