  We report on the polarization properties of two fast radio bursts (FRBs):
151230 and 160102 discovered in the SUrvey for Pulsars and Extragalactic Radio
Bursts (SUPERB) at the Parkes radio telescope. FRB 151230 is observed to be 6
$\pm$ 11% circularly polarized and 35 $\pm$ 13 % linearly polarized with a
rotation measure (RM) consistent with zero. Conversely, FRB 160102 is observed
to have a circular polarization fraction of 30 $\pm$ 11 %, linear polarization
fraction of 84 $\pm$ 15 % for RM = -221(6) rad m$^{-2}$ and the highest
measured DM (2596.1 $\pm$ 0.3 pc cm$^{-3}$) for an FRB to date. We examine
possible progenitor models for FRB 160102 in extragalactic, non-cosmological
and cosmological scenarios. After accounting for the Galactic foreground
contribution, we estimate the intrinsic RM to be -256(9) rad m$^{-2}$ in the
low-redshift case and $\sim 2.4 \times 10^{2}$ rad m$^{-2}$ in the
high-redshift case. We assess the relative likeliness of these scenarios and
how each can be tested. We also place constraints on the scattering measure and
study the impact of scattering on the signal's polarization position angle.
