Ignoring them is the best policy that I can think of because you certainly cannot trust them. I'm going to list the extent of my experience with beggars, and if you had my experiences I think you would not trust them either.
In my hometown an article came out that a large number of them were not poor and did not need to beg people for money. They merely lived off the system, some of them on disability/workers' compensation were walking the streets begging for money. In one case, a woman was found guilty of pan-handling when she pretended to be homeless, but in reality she owned an APARTMENT building. I once gave a guy $20 to go get some food, and watched as he went across the street to a bar and bought beer. Later this same dude actually went into a church and was begging people for money during a service. When he didn't get any from those in the church, he called my mother a whore and left. At the bus station I got approached by a guy who was better dressed than I was and he begged me for some money. I took one look at him and told him to f*ck off.
So yeah, not a big fan of charity in their cases because a lot of them aren't even poor.