Pete Morrison from Suvudu writes about why he suspects that the rebels main ship “The Ghost” is a pirate ship:
This leads me to an interesting train of thought. If this ship isn’t Imperial than what could it be and why would the “heroes” of our show be attacking it? The most logical answer is that it is private shipping either freight or passenger. It could be a ship owned by Sienar Fleet Systems or another firm that is transporting goods through or from Lothal.It would make sense for these ships to show up among Star Destroyers and TIE fighters if the Empire after an attack by pirates was to start providing more protection for shipping.We know that pirates love to decorate their crafts with the emblem of their particular group. The Ghost features to images on its hull. Neither of which I can find previously existing in canon.There is also the fact that the Rebel Alliance Starbird logo that HASBRO has revealed as part of its packaging looks different from the traditional Alliance Starbird and has some interesting stylistic similarities to the Novahawk which was the emblem of Rebel Privateers.
Source: Jedi News