  It has been recently proposed that the observed 511 keV emission from the
Galactic bulge could be the product of very light (1-100 MeV) annihilating dark
matter particles. Other possible explanations for this signal are associated
with stellar objects, such as hypernovae. In order to distinguish between
annihilating light dark matter scenario and more conventional astrophysical
sources for the bulge emission, we here propose the study of dwarf spheroidals
such as Sagittarius. These galaxies have typical luminosities of $10^5 L_\odot$
but mass-to-light ratios of $\sim 100$. As there are comparatively few stars,
the prospects for 511 keV emission from standard astrophysical scenarios are
minimal. The dwarf spheroidals do, however, contain copious amounts of dark
matter. INTEGRAL/SPI has observed the Sagittarius region. Analysis of this data
for 511 keV emission will provide a test of MeV dark matter which can
distinguish between annihilating dark matter and more standard astrophysics.
The observation of such a signal from Sagittarius should be a ``smoking gun''
for MeV dark matter.
