The holiday is commonly printed as Veteran’s Day or Veterans’ Day in calendars and advertisements. While these spellings are grammatically acceptable, the United States government has declared that the attributive (no apostrophe) rather than the possessive case is the official spelling. [Link]

I just came across this while completing an on-line survey for Ruby Tuesday:

Short story – someone “corrected” a UPS billboard at Grand Central Terminal by adding an unnecessary apostrophe.

I wrote about it on my own blog.