  In this paper, we perform a detailed analysis on the same-sign dilepton
signature in the inert doublet model. Focusing on the low dark matter mass
region, we randomly scan the corresponding parameter space. Viable samples
allowed by various constraints are obtained, among which twenty benchmark
points are selected for further collider signature study. At hadron colliders,
the same-sign dilepton signature is produced via $pp\to W^{\pm *}W^{\pm *}jj
\to H^\pm H^\pm jj$ with the leptonic decay mode $ H^\pm \to HW^\pm (\to l^\pm
\nu)$, where $H$ is the dark matter candidate. We investigate the testability
of this signal at the high-luminosity LHC (HL-LHC) and the proposed 27 TeV
high-energy LHC (HE-LHC). According to our simulation, the HL-LHC with
$\mathcal{L}=3~ab^{-1}$ can hardly probe this signal. Meanwhile, for the HE-LHC
with $\mathcal{L}=15~ab^{-1}$, it is promising to obtain a $5\sigma$
significance when $250~\text{GeV}\lesssim m_{H^\pm}-m_H\lesssim 300$ GeV with
dark matter mass $m_H\sim 60$ or 71 GeV.
