  Asteroid-mass primordial black holes (PBH) can explain the observed dark
matter abundance while being consistent with the current indirect detection
constraints. These PBH can produce gamma-ray signals from Hawking radiation
that are within the sensitivity of future measurements by the AMEGO and
e-ASTROGAM experiments. PBH which give rise to such observable gamma-ray
signals have a cosmic origin from large primordial curvature fluctuations.
There must then be a companion, stochastic gravitational wave (GW) background
produced by the same curvature fluctuations. We demonstrate that the resulting
GW signals will be well within the sensitivity of future detectors such as
LISA, DECIGO, BBO, and the Einstein Telescope. The multi-messenger signal from
the observed gamma-rays and GW will allow a precise measurement of the
primordial curvature perturbation that produces the PBH. Indeed, we argue that
the resulting correlation between the two types of observations can provide a
smoking-gun signal of PBH.
