From Halopedia, the Halo wiki
The Keyboard Emoticons is an easter egg in Halo: Combat Evolved Anniversary's campaign. It appears as additional buttons on a keyboard, with "^_^", "o_O" and ">_<" eastern style emoticons on it.
It can be found in Cryo B control room, on the control panel's keyboard. To see the Easter Egg, the player must be in the new graphics, not classic mode.