About two years ago, my wife saw a woman in the parking lot of a large retail grocery/goods store holding a sign that said "anything helps". She had noticed this woman before on at least one occasion, and it occurred to my wife that perhaps this time she would do something to help somebody out.
In addition to the things she needed, she purchased everything required for a large spaghetti dinner to include Parmesan cheese, a large loaf of fresh bread, and a box of cookies for dessert. She ensured everything was bagged up separately so all she had to do was hand it to the woman with the sign.
After loading up our car, my wife drove over to the woman in the sign. She got out with the bag and as she walked towards the sign-holder, explained "hey, I just wanted to help out so I bought you everything for a dinner..." to which the woman replied, "food's not really our issue."
My wife told me that she essentially closed her still-open mouth, did a 180 and got back into the car. We had spaghetti that night.
I relate this not to imply that everybody with a sign implying need is a fraud, but to suggest that there may be a non-trivial number of people out there who do not act because they've had an experience similar to the one my wife had.