While not technically a free agent signing, ESPN reported the complexities of Damarius Randall's option year.

Apparently they have until May 3rd to declare if they will pick up the 5th year option on his rookie contract (or he would become a free agent next year). The NFL formula pegs his salary on the 5th year option at $8.526M.
If they exercise the option, his salary is guaranteed against injury, but they could still release him prior to the first day of the league year (in 2019) without consequences.

They did exercise the option on Ha Ha, but did not on Nick Perry, who they eventually just resigned. It will be interesting to see what they do.