
AC: Altaïr assassinating William of Montferrat.

AC2: Ezio performing a leap assassination.

AC Brotherhood: The assassination of Cesare Borgia.

AC Revelations: Ezio burning ships with Greek Fire.
So far, each Assassin's Creed game has contained hidden messages from Subject 16 in various forms. In the end of AC1 (and beginning of AC2), it is possible to see a massive mural and various drawings within Desmond's cell and around the Animus.
In AC2, Subject 16 left behind glyphs that, when inspected very closely, contained various types of codes. Codes such as Morse, binary, Ceasar shifts and pigpen ciphers. In AC2: Brotherhood, the glyphs have evolved into "rifts", but work much like the glyphs do.
Each message comes with my personal notes (based on internet searches) of what they could mean. Each code also come with a solution.
Glyphs 3, 4, 6: 'Descendants', 'Infinite Knowledge' and 'Brothers'
Glyphs 8, 10, 11: 'Martyrs', 'Apollo' and 'The Inventor'
Glyphs 12, 17, 19: 'Titans of Industry', 'The Bunker' and 'The Fourth Day'
In the waitingline...
This game doesn't have hidden messages. But it has bugs.
10 bugs found