I always use the Glider (Hacker's Emblem) as my wallpaper (from this Deviantart artist), it makes a great minimalist dark background: http://mientefuego.deviantart.com/art/Carbon-Glider-12926852...

Minimal representation (using 2 Braille Unicode characters) is: ⠠⠵

But Apple's version contains a single cell in the top right that will interact with the Glider and will mutate and become a static structure 4 iterations later. I tested in this html5 Conway's Game of Life online simulator: http://www.quesucede.com/public/gameoflife/game.html