  Common models of blazars and gamma-ray bursts assume that the plasma
underlying the ob- served phenomenology is magnetized to some extent. Within
this context, radiative signatures of dissipation of kinetic and conversion of
magnetic energy in internal shocks of relativistic magnetized outflows are
studied. We model internal shocks as being caused by collisions of homogeneous
plasma shells. We compute the flow state after the shell interaction by solving
Riemann problems at the contact surface between the colliding shells, and then
compute the emission from the resulting shocks. Under the assumption of a
constant flow luminosity we find that there is a clear difference between the
models where both shells are weakly magne- tized ({\sigma}<\sim0.01) and those
where, at least, one shell has a {\sigma}>\sim0.01. We obtain that the
radiative efficiency is largest for models in which, regardless of the
ordering, one shell is weakly and the other strongly magnetized. Substantial
differences between weakly and strongly magne- tized shell collisions are
observed in the inverse-Compton part of the spectrum, as well as in the
optical, X-ray and 1GeV light curves. We propose a way to distinguish
observationally between weakly magnetized from magnetized internal shocks by
comparing the maximum frequency of the inverse-Compton and synchrotron part of
the spectrum to the ratio of the inverse-Compton and synchrotron fluence.
Finally, our results suggest that LBL blazars may correspond to barely
magnetized flows, while HBL blazars could correspond to moderately magnetized
ones. Indeed, by comparing with actual blazar observations we conclude that the
magnetization of typical blazars is {\sigma} <\sim 0.01 for the internal shock
model to be valid in these sources.
