I have been using this test since cigarettes went over five dollars a pack. The dynamic is, that since a rock of crack or a hit of heroin each run $10, and that a drug addict devotes his life to scrounging for that figure, any purchase over $5 is totally beyond the dope fiend pale. Lowlifes have always used cigarettes, usually a request for a free one or a light, as a means of getting close to someone they may want to shakedown, rob, or attack.
Ever since the price of smokes in Maryland has topped $5, begging for cigarettes has doubled. But, the big thing was that people began asking to buy a single cigarette for a quarter, and then for 50 cents, as they simply lacked the discipline to save up more than $5 and not bypass tobacco for better dope, resulting in their $5.40 to $7 pack of smokes costing $10.
In Baltimore and Central Maryland most crackheads and heroin addicts also smoke cigarettes, and usually not as regularly as an ordinary smoker, until they have kicked the hard dope and go full bore three packs a day into the tobacco. Currently, my neighborhood is host to about two dozen heroin addicts, who are the privileged children of successful white flight settlers who own homes in Harford County, and are about my age. These barely privileged kids do not have the funds to be dope fiends the suburbs, so they are pioneering in groups homes dedicated to drug use, resettling the areas their parents fled from. In my area all of these types play the single cigarette game.
As for the black community, you will note that almost every unattached adult male wants to buy cigarettes, an indication that vast numbers of urban black men are crack and heroin users.
My best guess is that if you assume that the person trying to buy a smoke is a crack head or dope fiend, then you will be correct three out of four times.