In December, Seattle signed the top free agent on the market when they inked second baseman Robinson Cano to a 10-year deal worth $240 million. The most notable moves they have made since have been signing 1B/OF Corey Hart to a one-year deal and trading for 1B/OF Logan Morrison.
What a "major" move might be depends on one's own personal definition, but it is likely safe to say that players like Ervin Santana, Ubaldo Jimenez, Bronson Arroyo, Matt Garza if his deal with Milwaukee goes awry, Nelson Cruz, Stephen Drew and Kendrys Morales would all probably fit into that category.
For now, the Mariners' management appears happy with the team they have formed. There is a good mix of veterans and youth as Cano, Hart, Franklin Gutierrez and more will join with still-developing (the Mariners might hope, anyway) players like Justin Smoak, Dustin Ackley, Michael Saunders and other younger players. Similarly, the pitching staff is led by Felix Hernandez and Hisashi Iwakuma and is starting to make way for the team's top-of-the-line pitching prospects as Taijuan Walker appears set to join the rotation full-time in 2014.
If Seattle does make another bigger move before the start of the upcoming season, it's more likely they will do so in a trade. The signing of Cano left the Mariners with two young, talented middle infielders for just one spot. Nick Franklin and Brad Miller were both rookies last season and held their own with Miller at shortstop and Franklin at second base. Both are highly-valued and could help bring in a decent return in a trade.
For now, however, the Mariners are content to make minor moves here and there. It may not yet be a team that can compete with the Rangers and Athletics in the AL West right now, but Seattle is setting itself up for success a few years down the line.