One such building, known as "B-18", is unmarked and tucked away in the storage area of a large federal building in Los Angeles. Human Rights Watch, the ACLU and other groups are trying to get the government to come clean about these detainment centers and where they are located.
From the Utne Reader: "Many of the centers still lack prominent signage, even in commercial buildings where businesses are well marked. One attorney who had a client held in a subfield office said the operations were 'akin to extraordinary renditions within the United States.'"