Valhalla wall Easter egg

The Valhalla Wall Easter Eggs are a series of "messages" that appear on the Halo 3 level, Valhalla.

Previously in Halo 2, if one were to change their date and clock on their console, one would find different signs for each date replacing the original "No Swimming signs" in Zanzibar. The same can be achieved on Valhalla, which has different messages located on the Forerunner Wall. These notes will not appear if you are on split screen.

In Halo: The Master Chief Collection, viewing two different sigils unlocks the Elder Signs achievement.

Variants
These can be accessed simply by changing the date on your Xbox 360.
 * January 1st (New Year's Day): Make Love Not War
 * April 22nd (Earth Day): A skull with a recycling sign.
 * May 5th (Cinco De Mayo): Toady Was Live!
 * July 4th: BBQ at Bob's Place (this is a reference to Marathon in which you kill BOBs or BOB-B-Qing).
 * July 7th (Bungie Day): Seventh Column Symbol.
 * October 31st (Halloween): A grave stone that has the initials "R.I.P.", meaning "Rest In Peace".
 * November 11th (Veteran's Day): Kilroy Was Here.
 * December 25th (Christmas): A Christmas light with an X on it.