If they are not an obvious fraud, I choose to err on the side of compassion by giving them a food gift certificate from a nearby restaurant -- McDonald's or whatever. I know certificates are converted easily into cash or traded for addictive substances, but that is an autonomous choice made by the recipient.
On a related subject, when I closely questioned the Prince George's Homeless Hotline (301-864-7140), they said that the rules they have been given to work under do not permit them to provide any services (and they have no other government or private social service referrals they can make) to "homeless" people who can not prove they have a PG County "home address." Let that sink in.
Then they told me that the D.C. Homeless Shelter (800-535-7252) will take anyone without any residence requirement (which I confirmed).
Of course, that is literally cold comfort this winter for those who find themselves "homeless" without a home address in Prince George's County.
Laurel Leader, Letters, January 26, 2007