Assassin insignia

The Assassin Insignia of the Assassin Order, though varying slightly over different time periods and countries, holds essentially the same shape and style. Each of its variations also possibly denote the various sects of the Order.

In Assassin's Creed, the insignia is used to mark the entrances of Assassin Bureaus, and is seen on the banners decorating the fortress of Masyaf. Within Assassin's Creed II, it is used on the mechanisms within the many Assassin's tombs, and on the banners and walls of Monteriggioni. In Assassin's Creed: Brotherhood, it is displayed on the banners hung in the Tiber Island Assassins Guild.

Additionally, it is worn openly on the armor and clothing of certain known Assassins, such as Mario Auditore, Ezio Auditore da Firenze and Nikolai Orelov.

The Insignia and the Assassins Hood
During the cinematic video of Assassin's Creed: Brotherhood, Ezio is seen in a close-up shot. During that shot, it is evident that his hood, which is a renewed itteration of the traditional Assassins hood from the original Assassin's Creed, bears a strong resemblance to the Assassins Insignia.

Trivia

 * In the Sanctuary, all of the statues have different Assassin insignias (Differing from their unique Assassin's Seals) on their waists, which are deviations of the original one. For example, Amunet's insignia bears two snakes.
 * In Brotherhood, Desmond searches for Assassin insignias painted onto the walls to guide him to the Colosseum Vault.
 * The insignia bears some resemblance to the symbol of the Freemasons.
 * The original insignia is not vertically symmetrical, unlike the Italian and Russian variations.
 * The original insignia is most likely influenced by the Greek letter "Delta." "Delta" is asymmetrical, and denotes change in mathematics. This fits well into the Assassins' goals.