FLOWERY BRANCH — The Atlanta Falcons signed running back Steven Jackson to a three-year, $12 million contract to firm up a soft spot in their offense. After their preseason opener, questions remain about the running game. Jackson, who was a free agent after rushing for at least 1,000 yards in eight consecutive seasons with the Rams, had five carries for 8 yards in a 34-10 loss to the Bengals on Thursday.