If you've been playing Assassin's Creed for a while, you already know that the 100 hidden feathers that litter the game are only the beginning of what the game offers obsessive collector-types. The real prizes are the Glyphs, 20 semi-hidden signs left plastered on certain landmarks, which were hacked into the Animus by the mysterious Subject 16. Once you've found them – which can be tough considering the size of some of the marked buildings – you'll then be tasked with solving a brief series of puzzles before you can crack the increasingly horrifying conspiracy story within.