  The PAMELA and Fermi measurements of the cosmic-ray electron and positron
spectra have generated much interest over the past two years, because they are
consistent with a significant component of the electron and positron fluxes
between 20 GeV and 1 TeV being produced through dark matter annihilation or
decay. However, since the measurements are also consistent with astrophysical
interpretations, the message is unclear. In this paper, we point out that dark
matter can have a more distinct signal in cosmic rays, that of a charge
asymmetry. Such charge asymmetry can result if the dark matter's abundance is
due to a relic asymmetry, allowing its decay to generate an asymmetry in
positrons and electrons. This is analogous to the baryon asymmetry, where
decaying neutrons produce electrons and not positrons. We explore benchmark
scenarios where the dark matter decays into a leptophilic charged Higgs boson
or electroweak gauge bosons. These models have observable signals in gamma rays
and neutrinos, which can be tested by Fermi and IceCube. The most powerful test
will be at AMS-02, given its ability to distinguish electron and positron
charge above 100 GeV. Specifically, an asymmetry favoring positrons typically
predicts a larger positron ratio and a harder (softer) high energy spectrum for
positrons (electrons) than charge symmetric sources. We end with a brief
discussion on how such scenarios differ from the leading astrophysical
explanations.
