Destination vacation

From Halopedia, the Halo wiki

Destination Vacation

Destination vacation is an achievement in Halo: The Master Chief Collection. It is unlocked by viewing one of the seasonal signs on Zanzibar in classic multiplayer.

The seasonal signs appear on New Year's Day (January 1), Bungie Day (July 7), Halloween (October 31), and Christmas (December 25). Players who don't want to wait for one of these dates can disconnect their console from Xbox Live, manually set their console to the desired date, then start the game and view the sign. Once the player reconnects their console to the internet, the achievement will unlock.