  We investigate a prospect of probing the type-III seesaw neutrino mass
generation mechanism at various collider experiments by searching for a
disappearing track and a displaced vertex signature originating from the decay
of $SU(2)_L$ triplet fermion ($\Sigma$). Since $\Sigma$ is primarily produced
at colliders through the electroweak gauge interactions, its production rate is
uniquely determined by its mass. We find that a $\Sigma$ particle with a mass
of a few hundred GeV produces a disappearing track signature from the decay of
its charged component, which can be searched at the HL-LHC. Furthermore, we
show that if the lightest observed neutrino has a mass of around $10^{-9}$ eV,
the neutral component of ${\Sigma}$ can be discovered at the proposed MATHUSLA
detector. We also show that the charged component of ${\Sigma}$ with a mass of
a few hundred GeV can be observed at the LHeC and FCC-he as a displaced vertex
signature.
