An apostrophe would give people the wrong idea of what Veterans Day is all about, says the U.S Department of Veterans Affairs (also no apostrophe).
According to their website, "Veterans Day does not include an apostrophe .. because it is not a day that 'belongs' to veterans, it is a day for honoring all veterans."
Fact is, veterans is not playing a possessive function in the phrase, Veterans Day; its function is attributive.
According to the Copyeditor's Handbook (notice the apostrophe) entry on attributive nouns, "The apostrophe is omitted when a plural head noun ending in s functions as an adjective, rather than as a possessor. In other words, when the relation between the plural head noun and the second noun could be expressed by the prepositions 'for' or 'by' rather than the possessive 'of.'"
So Veterans Day is a day for veterans, not a day of veterans. Okay, but just as this starts to make sense, the handbook goes on to say, "If the plural form of the head noun does not end in an s, an apostrophe is used."
Huh? That's almost as confusing as its and it's.
When language and its rules get weird like this, it's often a signal that the language is changing. Some uses of the apostrophe may be on their way out. A linguist in the article, "Apostrophe Sparks Veterans Day Conundrum" (11/07 The Missourian), calls the apostrophe "an overrated piece of punctuation."
Is the apostrophe really on its way out of the English language? Some people are actively trying to eliminate it, such as the author of killtheapostrophe.com, who writes, "It serves only to annoy those who know how it is supposed to be used and to confuse those who dont."
I once took a very important quiz on Quizilla, called "What Punctuation Mark are You?" I was really hoping I would be an apostrophe, but it turns out I'm a comma.
It's a good thing, too, since the apostrophe often falls victim to abuse, has so many enemies, and is looking at a rather tenuous future.