Da Vinci Code objects

The Da Vinci Code Objects are untextured objects that appear in some of Halo 3 's levels. These objects end up using a default texture: a grid of letters and numbers. The name was likely inspired from the default texture's slight visual similarity to the "cryptex" featured in Dan Brown's The Da Vinci Code.

Easter Eggs
  On Sandtrap and Sandbox, spherical untextured objects have been found. These objects, dubbed "easter eggs", are located near or inside large, tower-like Forerunner structures, and in both levels serve to keep the player from exiting the level.

Sandtrap
In Sandtrap, the Eggs fire orange beams into the sand whenever a player tries to exit the map; these beams activate Brute Landmines that are buried along the level's perimeter. The beams themselves are harmless unlike the beams on Sandbox. In both cases, the Eggs' kills are attributed to The Guardians.

To get a closer look at the Eggs in Sandtrap, you'll need to activate Pan Cam. Then you need to kill yourself making sure your body ends out of the map or is destroyed completely such as killing yourself while in Forge Mode. Then go to Theater and fly out of the map to any of the towers. The eggs will be near the top right of the towers.

Sandbox
In Sandbox, the Eggs fire subtler but more powerful beams directly at escaping players, killing such players almost instantly. The beams on Sandbox are also much more accurate as they were meant to target specific players. However, unlike Sandtrap, the beams can be blocked by most Forge Objects as well as Bubble Shields. These beams are very similar to Guass Rifle shots from a Guass Warthog.

To see the eggs, two players must cooperate. One player (Person A) must, while in Edit Mode, exit the map from the Sky Bubble by spawning a Teleporter outside of the map. Person A must then fly to a tower (but watch out for kill barriers) and spawn a turret against the light in the tower. A second player (Person B) must then man the turret and have Person A pick the turret up. Person A should drag Person B up the wall while B is still against it. Towards the middle of the light, the Easter Egg can be seen.

DaVinci Cube
 On the map Heretic, the DaVinci Cube is hidden inside each of the Grav-Lifts in the center of the map. To access the cubes, a turret must be placed right against the top of the Grav-Lift. Then a player needs to get on the turret. While on the turret, the player needs to look all the way and switch to Forge Mode. This will place them inside the small compartment that holds the DaVinci Cube.

The purpose of the DaVinci Cube on Heretic is to power the Grav-Lifts. If the map is overloaded, then the eggs will disappear which will disable the Grav-Lifts. The DaVinci Cube is a lot smaller than the Easter Eggs on Sandtrap and Sandbox. There are currently only 3 known DaVinci Cubes on the map Heretic. It is unknown why Bungie decided to use the DaVinci Cube to power the Grav-Lifts instead of the traditional methods like the way the lifts on Sandtrap are powered. It is possible that the DaVinci Cube has been used before in older maps like Valhalla but have not been found yet.

DaVinci Code Towers
 In Campaign, on the level The Covenant, there is a glitch that is able to force 3 DaVinci Code Towers to appear outside of the map. The only method capable of making these towers appear is by using the Time Travel Glitch. These towers do not appear in normal gameplay. These towers appear to be the shield generating towers that you must disable to continue through the mission. Nearly the entire tower is covered in DaVinci Code. However, unlike the other DaVinci Code Objects on the multiplayer maps, the DaVinci Code Towers are not solid and serve no immediate purpose.

These towers can only appear when the shields are still up and haven't been disabled. It is possible that Bungie programmed two versions of the tower or at least two layers. The outer layer stays the same and is always there. But the inner layer, the DaVinci Code Tower might be what is projecting the beam that powers the shields. So when you disable the shield generators the towers would disappear. All three DaVinci Code Towers are exactly the same. Since the towers are not solid, there is no way to walk on them.

Trivia

 * The default texture appears to be a UV-unwrapped image (used to help artists paint textures onto 3D models). The image consists of a grid, with each tile containing a letter of the alphabet.
 * The Sandbox Easter Eggs' beams can be blocked with Forge Objects, rendering the Eggs harmless; Bubble Shields also provide temporary protection.
 * More DaVinci Code Objects can be seen in the Halo 3 ViDoc "Et Tu Brute?".