  This paper analyzes astrophysical scenarios that may be detected at the upper
end of the energy range of the Gamma Ray Large Area Space Telescope (GLAST), as
a result of cosmic-ray (CR) diffusion in the interstellar medium (ISM).
Hadronic processes are considered as the source of $\gamma$-ray photons from
localized molecular enhancements nearby accelerators. Two particular cases are
presented: a) the possibility of detecting spectral energy distributions (SEDs)
with maxima above 1 GeV, which may be constrained by detection or non-detection
at very-high energies (VHE) with observations by ground-based Cerenkov
telescopes, and b) the possibility of detecting V-shaped, inverted spectra, due
to confusion of a nearby (to the line of sight) arrangement of
accelerator/target scenarios with different characteristic properties. We show
that the finding of these signatures (in particular, a peak at the 1--100 GeV
energy region) is indicative for an identification of the underlying mechanism
producing the $\gamma$-rays that is realized by nature: which accelerator (age
and relative position to the target cloud) and under which diffusion properties
CR propagate.
