I'm always a "little" skeptical about the ones holding the "Vietnam Veteran" sign and they're only 20 years old!!
My friend and I came up with a great idea - put together packets to hand to the homeless:
* list of resources w/addresses & phone numbers (like shelters, etc)
* 2 bus tickets (for city transit) so they can get to a shelter
* a bar of soap, toothbrush, and toothpast
* a note of encouragement
We figured that way the people who really need help could get to a shelter and find help - the scam artists wouldn't get our $$