The Bengals signed kicker Marshall Koehn. They waived safety Derron Smith in a corresponding move. Kicker Randy Bullock strained his back Monday, prompting the Bengals to sign Koehn as insurance. Koehn, a first-year player, originally signed with the Dolphins as a college free agent out of Iowa in 2016. Miami waived him before the start of the season, and he was not with a team last season.