I've been searching around for a couple of days to see if anyone noticed this. In Halo S02E07 around the 38 minute mark, Talia Perez is staring at her reflection just before Master Chief walks in to talk to her. Over the loud speaker, you can hear someone say "Tango-Hotel-Xray-one-one-three-eight". (headphones helps) That's a classic reference to George Lucas' early film THX-1138. Used heavily throughout the Star Wars universe and many other films.