Carved Letters in Sierra 117
From Halopedia, the Halo wiki
Sprinkled throughout the dense foliage of the first mission, Sierra 117, are carved hearts with initials and dates. Clearly, the overworked developers were feeling a tad guilty about their lonely wives and girlfriends at home. This can be seen throughtout all difficulties and requires normal gameplay (Using Forge is optional).
Watch the link below (Video is not in Youtube form)
>http://www.gamesradar.com/us/xbox360/game/features/article.jsp?articleId=20071026164528727088&releaseId=2005000000000000000350§ionId=1003&pageId=20071026172154848075