What were Persephone's symbols?

Answer 1

In Greek art, Persephone is invariably portrayed robed. She may be carrying a sheaf of grain.
General symbols are springs, wreaths of flowers worn in hair, torches, reeds, waterfalls, rivers, and spring.

Answer 2

Sheafs of grain : a goddess of Spring growing things; a tie to Demeter.

A flaming torch : a reference to her journey though the Underworld and bringing life to earth.

Asphodel : a field of this grows in the Underworld where the dead dwell.

Symbols of Hades were also considered hers, being the Queen of the Underworld.