"My other car is a Marza"
That's awesome! My friend saw that, smiled, pointed at the screen, and said I want it. He also suggested one with a picture of the Kol on it, but I'm not sure what it would say. I love your idea as well, Ryat (including the extra letters for effect).
As to using unit quotes, I suggest that after seeing a lot of shirts that do that with movies and games. It's become viral and it makes fans smile. A friend of mine told me that he saw someone wearing a shirt (I forget what it said) related to a game that he also played. So he walked up and said something to the shirt's owner in reference to that game. The other person laughed and nodded. They didn't even know each other, but that shirt created community. Whether it's a clever saying like "My other car is a Marza" or a very familiar unit effect from the game, we would promote this game and hopefully bring more people in, and we would come across other fans and have something to talk about. However, I don't think we should only do unit quotes. Definitely mix it up and have clever quotes, unit quotes, and shirts with graphics and simply the title: Sins of a Solar Empire on the back.