  We analyze a new signature of a charged Higgs boson in the Type-I realization
of the 2-Higgs Doublet Model (2HDM), where the mass of the charged Higgs boson
satisfies the condition $M_{H^{\pm}}<M_{t}+M_{b}$ and the theoretical parameter
space is consistent with the latest experimental constraints from Large Hadron
Collider (LHC) and other direct as well as indirect searches. In the surviving
regions, it is found that the bosonic decay mode of a charged Higgs boson is
dominated by $H^{\pm} \rightarrow W^{\pm*}h$. At the same time, the light
neutral Higgs boson $h$ dominantly decays into two photons. We thus find that
the production process $pp \rightarrow H^{\pm}h \rightarrow W^{\pm*}h h
\rightarrow l^{\pm}\nu +4\gamma$ is almost background free. Since the $W^{\pm}$
could be either off-shell or on-shell, furthering a previous phenomenological
analysis, we examine closely detector effects onto the above signature and
demonstrate that it is indeed promising to study it at the LHC with both
$\sqrt{s}= 13$ TeV and $\sqrt{s} = 14$ TeV, assuming an integrated luminosity
of 300 $fb^{-1}$.
