  We present calculations of molecular, atomic and ionic line emission from
simulations of giant molecular cloud (GMC) collisions. We post-process
snapshots of the magneto-hydrodynamical simulations presented in an earlier
paper in this series by Wu et al. (2017) of colliding and non-colliding GMCs.
Using photodissociation region (PDR) chemistry and radiative transfer we
calculate the level populations and emission properties of $^{12}$CO $J=1-0$,
[CI] $^3{\rm
  P}_1\rightarrow{^3{\rm P}}_0$ at $609\,\mu$m, [CII] $158\,\mu$m and [OI]
$^3{\rm P}_1\rightarrow{^3{\rm P}}_0$ transition at $63\,\mu$m. From integrated
intensity emission maps and position-velocity diagrams, we find that
fine-structure lines, particularly the [CII] $158\,\mu$m, can be used as a
diagnostic tracer for cloud-cloud collision activity. These results hold even
in more evolved systems in which the collision signature in molecular lines has
been diminished.
