Harvesting of "wild" ginseng is legal but only during a specific season defined by your state. It is also illegal to dig ginseng for export if the plant is less than 10 years old (CITES regs). The season is usually the autumn months and requires you to be aware of other federal regulations for harvesting on their lands. Currently, 18 states issue licenses to export it.
Lets identify Panax quinquefolius: American ginseng's three-pronged (or more) five-leaflet display of the mature plant can help you identify the plant (see above 5-proned wild ginseng photo). W. Scott Persons, in "American Ginseng, Green Gold", says the best way to identify "sang" during the digging season is to look for the red berries. These berries plus the unique yellowing leaves toward the end of the season make excellent field markers.