  Primordial black holes (PBHs) from the early Universe have been connected
with the nature of dark matter and can significantly affect cosmological
history. We show that coincidence dark radiation and density fluctuation
gravitational wave signatures associated with evaporation of $\lesssim10^9$ g
PBHs can be used to explore and obtain important hints about the formation
mechanisms of spinning and non-spinning PBHs spanning orders of magnitude in
mass-range, which is challenging to do otherwise.
