Spartan signals

Decades of fighting against an increasingly adaptive enemy has forced the Spartans to develop shorthand communications system for use against the Covenant. Many of these ideas are known and understood by the Spartans only, as well-guarded secrets. These also sometimes make normal conversations with the Spartans impossible, as they can do a great deal inside their MJOLNIR armor that is indistinguishable from the outside.

Oly Oly Oxen Free
Oly Oly Oxen Free is the Spartans' best-kept secret. It is their all clear signal which virtually no non-Spartan knows; the only known surviving non-Spartans being Cortana (Master Chief's 'personal' AI) and Doctor Halsey ("programmed" the Spartans). Deja also knows it, as she taught this to them, though her fate is unknown as she was situated on the now conquered Reach. This allows them to use it with guarded impunity over the COM to make others aware of their presence, location, or as an all-clear signal. It is a simple six note tune that can be whistled.

Spartan "Smile"
Having grown up as soldiers, the Spartans kept their emotions to themselves, always controlling "bursts of emotion". The closest thing to an emotional symbol is the "Spartan smile," used in place of a smile. The Smile consists of a quick swipe of a smile across ones own faceplate or a teammates with one or two fingers. The former was usually used in place of the latter.

Open COM
The Spartans signal to one another to open private COM frequencies by the flick of a finger. It is a move performed only in non combat situations, when the Spartans can pay attention to one another's movement. This way they can talk to one another without any external people hearing their conversation.

Attention
The Spartans will click a COM channel twice to get the attention of their teammates if they need assistance. Recent improvements in Covenant sensor technology have made this gesture increasingly impractical, as Covenant will be made aware of a Spartan's location if that Spartan uses the COM in the presence of a Covenant Vehicle.

Relax
The Spartans sometimes console one another nonverbally with a simple bump of the shoulder. They have become used to their MJOLNIR armor, and so each move they make is deliberate. Hence, the gesture is easy to recognize and understand.

Trouble Ahead
The Spartan scouts signal trouble ahead with a slight shake of the head from side to side.

"Stay Cool"
A short lateral cut with the hand signals to stay calm.

Inspect Armor
By making a circle in the air with an index finger to turn around, a Spartan signals that they want to visually inspect another Spartan's armor. Even if the computer diagnostics report everything as fine, Spartans don't take chances with their armor.

Come Forward
In combat, Spartans motion one another forward by flashing an index finger twice.

Wait
Spartans tell one another to wait by flashing an amber acknowledgment light twice on their HUDs.

Retreat
Spartans signal one another to retreat immediately by winking three red acknowledgment lights on their HUDs.

Friendly Approaching
On the battlefield, verbal communication could risk giving away one's position. Therefore, Spartans inform allied positions that they are approaching by winking their acknowledgment lights green twice.

Freeze
Slowly making a fist signals a Spartan team to freeze.

Finger
It has been noted in the book "Ghosts of Onyx" that Kelly makes "An ancient and arcane gesture with one finger" to the sentinels. This could possibly be the same as today's middle finger.

Welcome
Spartans "welcome" one another by swiping two fingers over their faceplate. This is a smooth, silent way to say hello, and is a toned down version of the Spartan-II's "Spartan Smile."

Unknown Ahead
Spartans on patrol who spot something ahead that is not immediately discernible as ally or enemy will signify it to their teammates by making a hand signal with a thumb pressing into the palm and the other fingers inwardly curled.