Offline Method:This method involves changing the date/time of your console. If you do not agree with this method, an online method is included below.
1. Go to "My Games & Apps" > "Apps" > "Settings" > "Network" and then "Go offline" & "Forget Wireless Network"
2. Hard reset your console by holding the power button for 5-10 seconds.
3. Sign in and go to "My Games & Apps" > "Apps" > "Settings" > "System" and then change the date to any of the follow dates:
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 (Independence Day): BBQ at Bob's
July 7th (Bungie Day):
October 31st (Halloween): A grave stone that has the initials "R.I.P."
November 11th (Veteran's Day): Kilroy Was Here
December 25th (Christmas): A Christmas light with an “X” marked through it
4. With the changed date, load Halo MCC, select a custom game in Halo 3 on Valhalla.
5. Go to the turret side and look at the white sign/symbol on the large metal wall.
6. Go to your settings and change the date again to another one listed above.
7. Go back into Halo MCC, and view the new sign on the wall in the Halo 3 map.
8. Go to "My Games & Apps" > "Apps" > "Settings" > "Network" and connect to your wireless connection by selecting it and entering the password. The achievement will unlock as soon as your Xbox connects to Xbox Live.
Online Method:This achievement requires you to view two date specific signs on the multiplayer map Valhalla in Halo 3. The date are as follows:
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 (Independence Day): BBQ at Bob's
July 7th (Bungie Day):
October 31st (Halloween): A grave stone that has the initials "R.I.P."
November 11th (Veteran's Day): Kilroy Was Here
December 25th (Christmas): A Christmas light with an “X” marked through it
On one of these days, in your local timezone, you will need to load a custom game in Halo 3 on Valhalla, and then go to the turret side and look at the white sign/symbol on the large metal wall. On the dates listed above, the sign will be unique and the achievement will unlock after viewing two of them!