  We calculate the flux and spectrum of synchrotron radiation produced by high
energy electrons and positrons (\epm) in an advection dominated accretion flow
(ADAF) around a black hole. The \epm are from the decay of charged pions which
are created through proton-proton collisions. We consider both a thermal and
power-law energy distribution of protons, and show that the resulting \epm
synchrotron emission produces a characteristic spectrum between radio and X-ray
frequencies. While previous signatures of the hot protons were only possible at
gamma-ray energies, via the production of gamma-rays through neutral pion
decay, the present results provide a more observationally tractable way of
probing the proton energy distribution and the two temperature structure in
these accretion flows. We discuss a number of strong observational predictions
from these systems, as well as the recent results of Mahadevan (1998) which
appear to confirm the two temperature structure in ADAFs. We show that the
results provide support for both a power-law and thermal distribution of
protons, with at least a third of the viscous energy going into the power-law.
