UPDATE: Trade is completed, per Joe Reedy.
After announcing their 53-man roster that included only three safeties on the team's roster -- with Chris Crocker being the lone free safety -- Adam Schefter reports that the Bengals are a finalizing a trade between cornerback David Jones and safety Reggie Nelson.
Nelson, a 2007 first round pick out of the University of Florida, recorded a career-high 70 tackles in 2009, playing in all 16 games. With seven career interceptions and 20 passes defensed, Nelson seems like he'd be a good addition on a team short of safeties. And of those safeties that are on the team, all of them suffered a minor injury at some point during the preseason.
I would still expect the Bengals to engrossed in the league's waiver wire to find more help.