Listening to radio show host Mike McConnell, he had two points that bear repeating regarding this particular type of person:
1) Real homeless advocates strongly advise not handing money over to these folks, because they more often than not just blow it on drugs/alcohol, because it encourages that the behavior continues, and because there are ample shelters willing to take care of them, so it's likely that they have burned a bridge if not allowed to stay in a given shelter for a justifiable reason.
2) Consider that people in these situations are often (but not always) people who have taken a **** on every person in their lives who ever loved or cared about them, and financing a continuation of their behavior is doing these people no favors, when they should instead be forced to confront their situation and make amends.
McConnell spoke from experience regarding the second point, having had twin sisters, one of whom had achieved much in life, while the other had taken a **** on her entire family repeatedly, with predictable results.
I just want to say something about homelessness. My brother was homeless for decades. Our family thought he was dead because we lost all contact with him, and hadn't heard from him in 40 years. He had PTSD from his service in Vietnam. Many homeless people have some kind of mental illness, such as severe PTSD, which prevents them from functioning in society.
No matter how compelling the panhandler's sign, if you feel compelled to help, consider instead donating to an organization that helps homeless people get back their lives.
I feel a great debt of gratitude for the charity that adopted my brother and helped him get his life back, and helped him find his family. He passed away last year, just 5 years after we were reunited. One of the greatest moments I've ever experienced, was to see the look of satisfaction on his face the last time I saw him. This could not have happened without the compassionate people who knew how to help him learn to function again.