Motors and Motion
If we had to pick one symbol to best represent the strike and Galt's values, we'd go with motors. Galt kicks off his strike by declaring that he'll "stop the motor of the world." He is also the nearly legendary inventor of "the motor" that Dagny discovers. This motor starts Dagny on a quest, which leads her to Galt and his strike. Apart from everything else he is, Galt is always mainly the "inventor of the motor" for Dagny:
But she knew that there was no meaning in motors or factories or trains, that their only meaning was in man's enjoyment of his life, which they served....She turned to Galt....She was looking at the inventor of the motor, but what she saw was the casual, easy figure of a workman in his natural setting. (188.8.131.52-76)
Motors serve as an expression and an embodiment of a certain philosophy here. Galt is fittingly the inventor of both the motor and a philosophical system that is embodied by motion.
Motors and movement are also closely linked to other characters in the strike. Dagny in particular is tied to motion; it's no coincidence that she runs a railroad. Both Dagny and Hank can fly airplanes, and we also see scenes of both of them driving cars. Motors and motion make up a major part of the values and the world of the strikers.