  We investigate the circular motion of charged test particles in the
gravitational field of a charged mass described by the Reissner-Nordstr\"om
(RN) spacetime. We study in detail all the spatial regions where circular
motion is allowed around either black holes or naked singularities. The effects
of repulsive gravity are discussed by finding all the circles at which a
particle can have vanishing angular momentum. We show that the geometric
structure of stable accretion disks, made of only test particles moving along
circular orbits around the central body, allows us to clearly distinguish
between black holes and naked singularities.
