When Chin is interviewing Gloria, on the wall behind him is a "Butterfly Love" poster on it. This is the same poster which hang in the room of the Brady Bunch girls for years.
At the 41 minute mark, while investigating the suspect's apartment, McGarrett glances at a couple paperback books. The top one is A Shade of Difference by Allen Drury, the 1962 sequel to his 1960 Pulitzer Prize winning novel Advise and Consent.
The title describes the practice at paid activities such as sporting events, skating rinks, amusement parks that allow the female half of a couple to have free admission as an advertising gimmick to attract couples or dates on outings.
Although he has a somewhat major role in the show, Soon-tek Oh is listed in the "supporting characters" section of the end credits.