Handing a person you don't know a hamburger isn't a solution to his problem. It is a very nice thing to do for McDonald's and may temporarily soothe your conscience.
If you really want to help that person, eat the burger yourself and buy that unknown person one of those "Chicken Soup For The Soul" books.
How do you identify those in real need from those
who gather money on a tax-free basis and make $60,000/year in a "poor-person" disguise---or borrow babies from their neighbor to get sympathy at a prime location for begging--- or those on drugs or alcohol looking to get to the next day at everyone else's expense?
I rely on reputable charities to make that distinction. I can't.