Jedi Assassins were a select group of Jedi padawans from the Calox III Jedi Academy who were taught to draw on the Force (light and dark) to find and destroy the Sith. They were trained in secret, as the Jedi Council was against using the dark side of the Force to achieve its goals.
These "Jedi Assassins" also had their own symbol which was very familiar to the Jedi Order Symbol. However there were some key differences. For example a flame is present in the center of the symbol.