Credit to Arizona Phil at the Cub Reporter for unearthing three minor league free agent signings that I have not seen anywhere else:
The three recent signees are veteran catcher Mark Johnson, ex-SF AA LHRP Jason Waddell, and ex-DET AA RHRP Angel Castro.
Only Johnson has major league experience; here's his career record. Johnson spent four years as a backup/semi-regular catcher for the White Sox; he was on their 2000 AL Central champion team, but did not play in the postseason. He doesn't hit much, but does hit lefthanded. Of his 16 career homers, two were hit in Wrigley Field. He's likely signed as insurance against Henry Blanco going elsewhere.
The other two are probably Triple-A roster filler.