Hester posted a photo of his new locker to Instagram on Tuesday night. In the caption, he referenced entering "another chapter in my book of life."
Hester averaged 7.2 yards per punt return on the season (17th in the NFL) and 24.5 yards per kickoff return.
Fox Sports earlier reported Hester's deal with Seattle.
The Seahawks have had a hole at this spot after Tyler Lockett suffered a broken leg in Week 16. J.D. McKissic and Paul Richardson handled kickoff returns for Seattle last week; Richard Sherman returned punts.
Hester, 34, holds the NFL record with 20 return touchdowns: a record 14 on punts, five on kickoffs and one return of a missed field goal.
ESPN's Jamison Hensley contributed to this report.