"A pair of heavy glass doors with 'M' etched on either leaf slid open, allowing the three utilitarian and drably dressed men, wearing the same stiff gray uniform bearing no markers of glory or striving performance on their monotonous surfaces but different in shape and background, to continue down the near sterile corridor." -- Chapter 2
The inspiration of the M's etched upon the glass doors of the spaceship Bethlem derives from the asylum by the same name. Upon the main entrance to the hospital was the carving below: Melancholia and Mania (Madness). Such, it is that each door the crew of the Bethlem passes through brings them further into the open embrace of Melancholy and Madness.