  In this article, we report a new signature of dark matter annihilation based
on the radio continuum data of NGC 1569 galaxy detected in the past few
decades. After eliminating the thermal contribution of the radio signal, an
abrupt change in the spectral index is shown in the radio spectrum. Previously,
this signature was interpreted as an evidence of convective outflow of cosmic
ray. However, we show that the cosmic ray contribution is not enough to account
for the observed radio flux. We then discover that if dark matter annihilates
via the 4-e channel with the thermal relic cross section, the electrons and
positrons produced would emit a strong radio flux which can provide an
excellent agreement with the observed signature. The best-fit dark matter mass
is 25 GeV.
