According to Paul Kuharsky, LB Caleb Campbell has reported that he is signing with the Colts:
On Facebook, LB Caleb Campbell indicates he's joining
Due to the Army calling in his service time, Campbell has played only one season (2010) in the NFL, despite being drafted in 2008. He was on the Detroit Lions' practice squad for the majority of last season, but was activated during the last four games of the season. He saw the field in three of them.
It has not been released whether Campbell was signed to the Colts' roster or to the practice squad. One thing that would point to the practice squad is the tweet of Chris Brooks earlier today. As I pointed out at the time on Twitter, it looks like Brooks is leaving the Colts, although it is unknown whether it is due to a cut or signing with a new team. In my opinion, Brooks would have been excited to share the news of a new team, but who knows?