Via Starwars.com:

HERE’S HOW TO IDENTIFY THE REBEL ALLIANCE, THE FIRST ORDER, AND MORE.
Do you remember the first time you noticed the symbols of the Empire and Rebellion appear in the original trilogy? The Imperial insignia can be seen on uniforms, and the Rebel Alliance starbird appears on the helmets of the X-wing pilots who take on the Death Star. Symbols like those appear throughout the Star Wars universe in the films, television series, books, games, and comics. Like emblems in our world, the symbols allow you to tell which organization someone has pledged his or her allegiance to with a quick glance. Here are five such symbols from the galaxy far, far away:

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