By moving around the menu areas you can find the following hidden messages.

Main menu
Upper left: "In the end, It all comes down to just one little thing..."
Bottom right: "Unity after death, Unity forever."

Single Player menu
Upper left: "Your body now, Our body later, One body forever"

Multiplayer menu
Upper middle: "It's not over between us, you can't run from me forever"
Bottom middle Make us Whole"

Quick Match menu
Bottom right: "We must believe in it and bend ourselves to its will and then it will heal us"

Leaderboard menu
Right: "The answer is in chicxulub"

Extra menu
Left: "Welcome back Nicole Brennan"

Controller Map menu
Bottom right: "Let us fear nothing. Death is only a transition to the unity beyond"