Symbolism, Imagery, Allegory
A bunch of the symbolism in Antigone lies in the characters themselves. Antigone and Creon represent a number of opposing forces: male vs. female, family ties vs. civic duty, man vs. nature, and man's laws vs. the laws of the gods. Phew! Also, there's the blind prophet Teiresias... who could be seen as representing the will of the gods.
But make sure to check out the meaty "Character Analysis" sections for more deets on the larger symbolism of the characters.