Fox and Martis, along with outfielder Brandon Boggs, receive non-roster invitations to Spring Training as part of their deals. The other three signees -- right-handed pitchers Kyle Cofield and Jose Diaz and infielder Stefan Welch -- will all report to Minor League camp next spring.
Fox, 29, was removed from Baltimore's 40-man roster last month after appearing in only 27 games with the Orioles in 2011. He hit .246 with two homers in those appearances.
Fox has played in 193 games and hit .237 over parts of four seasons in the Majors. Though his success in the big leagues has been minimal, Fox has always hit for power in the Minors. Defensively, Fox has shown an ability to play all over the field, including both corner infield spots. He started his professional career as a catcher and also has played extensively in the outfield.
Martis, 24, last appeared in the Majors with the Nationals in 2009, posting a 5.25 ERA over 15 starts. He spent 2010 pitching out of the club's Triple-A rotation and started for Washington's Double-A squad last year.
In 23 Double-A starts, Martis went 8-6 with a 3.05 ERA.
While he may have stalled some as a starting pitcher, the Pirates are likely to look at Martis as a relief option during Spring Training competition.
Boggs, 28, has played in just 29 big league games since 2008, when he appeared in 101 as a rookie with Texas. Boggs hit .226 that season, and he has played all three outfield positions in the Majors. He left the Rangers' organization after the 2010 season and signed with the Brewers.
Boggs spent the majority of 2011 in Triple-A, where he batted .241 with 19 doubles, nine homers, 53 RBIs and a .381 on-base percentage in 94 games. The switch-hitter appeared in 16 games with Milwaukee.
Cofield, 24, has not yet dented a Major League roster, though he advanced as high as Triple-A during his 2011 season in the White Sox organization. Used exclusively as a reliever, Cofield posted a 2.89 ERA in 15 Double-A appearances before finishing the year with two outings in Triple-A.
An eighth-round Draft pick in 2005, Cofield was used largely as a starter in his first few years in the Minors.
Diaz, 27, has been pitching in the Minors since 2002, when the Dodgers signed the right-handed pitcher as a non-drafted free agent out of the Dominican Republic. He pitched in the Orioles' system each of the past two seasons.
In 48 combined relief appearances in Double-A and Triple-A in 2011, Diaz had an 0-3 record and a 2.52 ERA. He struck out 48, walked 21 and saved 27 games in 44 2/3 innings. This marked the first season in which Diaz had advanced as high as Triple-A.
Welch, 23, moved to Class A Advanced within the Mets' system in 2009 and has remained at that level since. In 2011, the Australia native batted .271 with 16 homers, 53 RBIs and 55 runs scored in 129 games.
Welch has played primarily as a first baseman since being signed as a non-drafted free agent in 2005. He has also logged a few games at third.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.