symbolically speaking, pluto/charon represent the dual nature of any soul that enters into this particular solar structure that we inhabit...
there's a glyph for pluto mentioned in alan oken's complete astrology (1988 bantam isbn 0-553-34537-0):

...(this) symbol expresses the entire concept of the regenerative processes of involution and evolution. the circle of spirit (during the involutionary process) emits its rays of life, which are then encased by the receptive nature of the soul (semicircle). the rays descend further, until they reach the plane of the earth, where they manifest into a particular physical form (the cross). in the reverse evolutionary process the experiences of physical life cause an awakening in consciousness. these realizations are assimilated in the soul and then transmuted into the ethers of the spirit, where they are integrated. then they are sent back down again through involution to further energize and develop the earth, nature, and man...