The Seahawks signed former Packers guard/center Greg Van Roten, as announced by Van Roten himself on twitter.
I've seen Packer fans question the move and Optimum Scouting and Draft Breakdown's Justis Mosqueda noted he is a 'solid offensive guard.'
According to Tom Silverstein of the Milwaukee Journal-Sentinel, Van Roten was "signed just before the start of training camp in 2012 out of Penn, [and] fought and clawed his way into contention for a roster spot, winding up on the practice squad to start the season. After five games, he was elevated to the 53-man roster and played in nine games, including two playoff contests. This year, the 6-3, 303-pound Van Roten didn't have as good of a training camp, but he played well enough that he was kept as a backup at both guard positions and center. He played on special teams each of the first three games but was inactive the next two."
So it looks like Seattle gets a prospect that has shown some promise and has some game, and playoffs, experience. It'll be interesting to see if he challenges for a roster spot come August.