It would seem that Microsoft had begun to add a ton of placeholder pages for Halo 4 DLCs to its XBox Live Store.
There are over a dozen of them in various names. These include:
Biddeford, Nobleboro, Waldoboro, Medomak, Warren, Thomaston, Rockland, Camden, Lincolnville, Northport, Belfast, Searsport, Stockton Springs, Bucksport, Orland, and Ellsworth.
The DLCs are listed as add-ons for Halo 4, in development at 343 Industries. Little else is known about these add-ons, save for the fact that they're (most probably) placeholder titles and not actual location or DLC titles seeing that they're names of real world locations. They'll be filled in with the proper details when the game comes out on November 6, so you'll just have to wait until then.
Halo 4 is set for a November 6 release and is exclusive to the Xbox 360.