  Raman scattering can detect spontaneous point-group symmetry breaking without
resorting to single-domain samples. Here we use this technique to study
$\mathrm{BaFe_2As_2}$, the parent compound of the "122" Fe-based
superconductors. We show that an applied compression along the Fe-Fe direction,
which is commonly used to produce untwinned orthorhombic samples, changes the
structural phase transition at temperature $T_{\mathrm{s}}$ into a crossover
that spans a considerable temperature range above $T_{\mathrm{s}}$. Even in
crystals that are not subject to any applied force, a distribution of
substantial residual stress remains, which may explain phenomena that are
seemingly indicative of symmetry breaking above $T_{\mathrm{s}}$. Our results
are consistent with an onset of spontaneous nematicity only below
$T_{\mathrm{s}}$.
