Baseball is a business, and, like most businesses, it shuts down for the holidays. It doesn't shut down completely, and you'll see moves on December 24th and December 26th, but rarely does anything happen on December 25th. According to MLB.com, since 2001 there have been zero Christmas day trades and just four Christmas day signings, which you'll find listed below.
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Minor league contracts with spring training invitations
(1) Luis Ugueto, 2004. You'll remember Ugueto as being the Rule 5 kid on the Mariners that one year. The best season of his career came in Tacoma in 2004, but he would then leave the organization by signing a minor league deal with the Royals. The infielder spent 2005 in AAA Omaha, and pitched once. It was a shutout inning.
(2) Abraham Nunez, 2004. There used to be two Abraham Nunezes. One of them could hit. This one couldn't. He wound up making the Cardinals in 2005, and was even all right, but he soon thereafter returned to normalcy, and posted a lifetime .627 OPS in the bigs and a .675 OPS in the minors.
(3) Keiichi Yabu, 2007. Everyone always remembers the good Japanese imports, but few remember the bad or mediocre ones. Yabu was moderately functional out of the Giants bullpen in 2008, but that was it for his big league career.
Major League contracts
(1) Jose Lima, 2004. Lima shook off four years of awful pitching to throw pretty well for the Dodgers in 2004. He then signed a seven-figure deal with the Royals and promptly spent the next season as one of the worst pitchers of all time, posting a 6.99 ERA that stands as the second-worst in the modern era for guys who threw at least 150 innings. This article, which announces the signing, begins "Christmas-time is now Lima Time," and it's a handy reminder that nothing is too sacred for the Royals to shit on.
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In conclusion, I don't have a conclusion. It's interesting that the Royals signed two guys on Christmas 2004 - either Allard Baird has a very understanding family, or he doesn't care for his family at all. What a post this turned out to be.