  Type IIP supernovae (SNe IIP) often show relatively high continuum
polarization ($\sim 1$\%) in the late phase. This polarization feature is
generally believed to be due to an inner aspherical core revealed in the late
phase, while this polarization feature can also be contributed by the effect of
polarized-scattered echoes by circumstellar (CS) dust around the SN. In this
paper, we propose a unique method to distinguish polarization from the SN
ejecta and from the light echo. We quantitatively examine wavelength dependence
of the polarization created by the scattered echoes for various geometries and
amounts of CS dust. It is found that the polarization in the $U$-band has
characteristic features, i.e., the polarization emerges at an earlier phase
with higher polarization degree than that in longer wavelengths. These are due
to the rapid evolution of the $U$-band light curve as well as higher optical
depth of dust in shorter wavelengths. Except for the $U$ band, the polarization
increases after the plateau phase, and the polarization degree is generally
higher for shorter wavelengths. These polarimetric features can be easily
distinguished from the polarization expected from an aspherical core, which
predicts almost no wavelength dependence. Moreover, we show that multi-band
polarimetric observations for SNe IIP can constrain a parameter space in the CS
dust mass and distance from the SNe. We thus encourage multi-band polarimetric
observations for SNe IIP.
