  Axionlike-particles (ALPs) are one promising type of dark matter candidate
particle that may generate detectable effects on $\gamma$-ray spectra other
than the canonical weakly interacting massive particles. In this work we search
for such oscillation effects in the spectra of supernova remnants caused by the
photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright
supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of
photon-ALP oscillations yields an improved fit to the $\gamma$-ray spectrum of
IC443, which gives a statistical significance of $4.2\sigma$ in favor of such
spectral oscillation. However, the best-fit parameters of ALPs
($m_{a}=6.6\,{\rm neV}$, $g_{a\gamma}=13.4 \times 10^{-11}\,{\rm GeV}^{-1}$)
are in tension with the upper bound ($g_{a\gamma}< 6.6 \times 10^{-11}\,{\rm
GeV}^{-1}$) set by the CAST experiment. It is difficult to explain the results
using the systematic uncertainties of the flux measurements. We speculate that
the "irregularity" displayed in the spectrum of IC443 may be due to the
superposition of the emission from different parts of the remnant.
