  We show here that orbital degrees of freedom produce a distinct signature in
the magnetic excitation spectrum of iron-based superconductors above the
magnetic ordering temperature. Because $d_{xz}$ and $d_{yz}$ orbitals are
strongly connected with the Fermi surface topology, the nature of magnetic
excitations can be modified significantly due to the presence of either static
or fluctuating orbital correlations. Within a five-orbital itinerant model, we
show that static orbital order generally leads to an enhancement of
commensurate magnetic excitations even when the original Fermi surface lacks
nesting at $(\pi,0)$ or $(0,\pi)$. When long-range orbital order is absent,
Gaussian fluctuations beyond the standard random-phase approximation (RPA)
capture the effects of fluctuating orbital correlations on the magnetic
excitations. We find that commensurate magnetic excitations can also be
enhanced if the orbital correlations are strong. Our results offer a natural
explanation for the incommensurate-to-commensurate transformation observed in a
recent neutron scattering measurement (Z. Xu, et. al., arXiv:1201.4404), and we
propose that this unusual transformation is an important signature to
distinguish orbital from spin physics in the normal state of the pnictides.
Implications for the magnetic and superconducting states are discussed.
