The Seahawks have placed a second-round tender worth ~$2.2M on restricted free agent safety Jeron Johnson.
Essentially, what this means is that Seattle has the right of first-refusal for any club that makes an offer on Johnson as a restricted free agent, and if the Seahawks fail to match that offer, they receive a 2nd round pick from the team that has made the higher offer. It also means that if no club is willing to give up a 2nd round pick for Johnson, which seems likely, Seattle would keep Johnson at that $2.2M salary. However, this offer sheet is not guaranteed (I believe), and Johnson could still be released or renegotiate a new contract with the Seahawks.
It's a bit surprising that Seattle placed a 2nd round tender on Johnson, a former UDFA that battled injuries all year before being placed on the IR in December. Because Johnson is a former undrafted free agent, the Hawks had to either place a first- or second-round tender on him, or place an original round tender on him would essentially make him a free agent -- with the stipulation that Seattle is given the right to match offers, but yield no picks if they decide not to match.
The Seahawks must value Johnson as a backup to Kam Chancellor and Earl Thomas, and as I wrote earlier today, backup safety isn't exactly the deepest position on the team with Chris Maragos set to enter unrestricted free agency.
The Seahawks placed original round RFA tenders on former undrafted free agents Clint McDonald and Clint Gresham last year worth ~1.3M, and neither player received better offers. Once the market (lack thereof) had been set, both were eventually brought back to the team on lesser deals; Gresham renegotiated a multi-year deal and McDonald was released then re-signed later to a one-year vet minimum deal.
Doug Baldwin and Lemuel Jeanpierre are also RFAs this season, so keep an eye out for what Seattle does there as well.