Just in case you don't speak Aurabesh, this translates to
“Enlist – The Empire is the Future.”
"Star Wars Rebels’ continues the epic tradition of the legendary ‘Star Wars’ saga with all-new exciting, action-packed adventures. It is a dark time in the galaxy, as the evil Galactic Empire tightens its grip of power from world to world. As the series begins, Imperial forces have occupied a remote planet, ruling with an iron fist and ruining the lives of its people.
But there are a select few who are brave enough to stand up against the endless Stormtroopers and TIE fighters of the Empire: the clever and motley crew of the starship “Ghost.” Together, this ragtag group will face threatening new villains, have thrilling adventures, and become heroes."
Star Wars Rebels will be with us sometime next year.