  We revisit the innermost stable circular orbits (ISCOs) of charged particles
and study the polarized images of synchrotron radiations emitted from such
orbiting hotspots on the equatorial plane in Schwarzchild-Melvin black hole
spacetime. We obtain a constraint on the magnetic field to retain ISCOs for
charged particles. In particular, we identify a critical value for the strength
of the magnetic field $B_c$ that the circular orbits can have positive and
negative angular momentums above $B_c$ while only one branch survive below
$B_c$. Furthermore, we investigate and discuss the primary and secondary images
of circularly orbiting charged hotspots carrying the information of
polarization directions observed by distant observers.
