The shirts were purchased by Mariners outfielder Mike Carp, a close friend of Halman's from their days coming up in the Minor Leagues together.
"It's just a reminder to not take life for granted," Carp said. "Value it. Appreciate it. It's just something guys can have in their lockers all year and keep him with us."
The shirts are orange, a tribute to the color of Halman's national team jersey in Holland. On the back, inscribed over his No. 56, is a Jackie Robinson quote: "A life is not important except in the impact it has on other lives."
The front of the shirts bear a logo of a Great Dane, another tribute to Halman's Dutch ancestry, with the words "Broer voor het leven," which translates to "Brother for life."
Carp said the shirts were the idea of Brodie Downs, a former Minor League teammate. Halman was stabbed to death on Nov. 21. Halman's brother remains in jail in Amsterdam after being arrested following the early morning incident in an apartment complex where the two were living over the offseason.
"Brodie designed them and asked if I could help out," said Carp, one of five Mariners players who flew to Holland for Halman's funeral. "I had a T-shirt guy back home, so [Brodie] sent me a couple demos, and I have a buddy who has a company and he pumped them all out. We're going to try to give them to the Minor Leaguers, too, because he has a lot of friends down there as well."
Carp said he's stayed in touch with Halman's family in the last few months and that his mom and sister both sent him messages after he posted a picture of the shirts on the Internet on Friday.
"She [Halman's mom] loved it," Carp said. "She said it was a great idea and a great thing to have a little something in his memory. She told me she'd be watching us this season and rooting for us."
Carp considered Halman his best friend and has more than the shirt to remember him by.
"I have him right here," the 25-year-old said, tapping the new tattoo on his left bicep. "He actually had this on his own arm. So when I went to Holland, his mom gave me a picture of it and I took it to my guy and had it put on in the same spot and everything.
"He'll be with me for the rest of my life."
The tattoo is a picture of a baseball surrounding both Europe and North America and says, "My world."
Carp added in two red stars, one in Amsterdam and one on the West Coast of the U.S.
The tattoo also includes Halman's favorite quote: 'No grind, no shine."
That work ethic and love of baseball is what has carried Carp through a difficult offseason. Following his friend's death, he got audio tapes of several of Halman's radio interviews and put them on his iPad.
"Every once in a while I flip it on and listen to him talk baseball," Carp said. "It's good motivation for me."
For Carp, the other motivation is to not let people forget his teammate. The shirts are one way to help in that effort.
"Not everybody knew him," Carp said. "We've got a lot of new guys, but there are young guys coming up that played with him and I figured this was a good way to keep his memory alive a little bit. Don't take things for granted. Tomorrow is never promised. It's a sad thing, but it's reality."
The Mariners are the first Major League team into Spring Training, reporting a week early due to their season opening on March 28-29 in Tokyo against the A's. Mariners pitchers and catchers reported for physicals on Saturday and will be on the field for the first time Sunday. Position players aren't due in until Friday, but Carp and some others have been in camp for several days working on their own.