If I saw someone ahead of me without a proper boarding order, I would make some noise and try to make sure proper boarding order is followed by forcefully bringing it up to the boarding agent. Since SW has open seating, I will take any empty seat, especially in the exit row, despite the fact that someone may be "saving" it. While a FA may not tell a sitting passenger he can not save a seat, she will also not prevent me from taking it. If I get on first, I am entitled to any open seat, and the saving passenger is only entitled to the one he is sitting in. Stand your ground.