  We consider cosmic string cusp annihilations as a possible source of
enhancement to the global background radiation temperature in $21$-cm photons
at reionization. A soft photon spectrum is induced via the Bremsstrahlung and
Synchrotron emission of electrons borne out of QCD jets formed off the cusp.
The maximal energy density background comes from synchrotron induced photons
with a string tension of $G\mu \sim 10^{-18}$. In this instance, the radiation
background at reionization is heated up by $5\cdot 10^{-3} \,\, K$. We find
that the depth of the absorption trough ($\delta T_b$) in $21$-cm at
reionization is altered by one part in $10^4$ from the strings, requiring high
precision measurements to be detectable. This mechanism cannot explain the
$\delta T_b$ observed by the EDGES experiment.
