  Emission from the photosphere in gamma-ray burst (GRB) jets can be
substantially affected by subphotospheric energy dissipation, which is
typically caused by radiation-mediated shocks (RMSs). We study the
observational characteristics of such emission, in particular the spectral
signatures. Relevant shock initial conditions are estimated using a simple
internal collision framework, which then serve as inputs for an RMS model that
generates synthetic photospheric spectra. Within this framework, we find that
if the free fireball acceleration starts at $r_0 \sim 10^{10}~$cm, in agreement
with hydrodynamical simulations, then the typical spectrum consists of a broad,
soft power-law segment with a cutoff at high energies and a hardening in
X-rays. The synthetic spectra are generally well fitted with a standard cutoff
power-law (CPL) function, as the hardening in X-rays is commonly outside the
observable energy range of current detectors. The CPL-fits yield values for the
low-energy index, $\alpha$, and the peak energy, $E_{\rm peak}$, that are
centered around $\sim -0.8$ and $\sim 220~$keV, respectively, similar to
typical observed values. We also identify a non-negligible parameter region for
what we call ``optically shallow shocks'': shocks that do not accumulate enough
scatterings to reach a steady-state spectrum before decoupling and thereby
produce more complex spectra. These occur for optical depths $\tau \lesssim 55
\, u_u^{-2}$, where $u_u = \gamma_u\beta_u$ is the dimensionless specific
momentum of the upstream as measured in the shock rest frame.
