One of the game's puzzles involves the phrase 'How Soon Is Now?' written on a wall with blood. The phrase is the title of one of The Smiths' most popular singles, and besides the obvious connection (all of the Killer 7 have Smith as a surname) the group is also one of director 'Suda 51''s favorite bands.
The courier pigeons found throughout the game are named after various girls from the James Bond films.
Iwazaru, Kikazaru, and Mizaru are meant to represent the three philosophical tenets of speak no evil, hear no evil, and see no evil, respectively. Their names are also the Japanese equivalent of the phrases.
The Pigeon memos are named after songs written by "The Smiths" (Still ill, Rusholm Ruffian, Well I wonder etc.)