  This Letter proposes a new signature for confining dark sectors at the Large
Hadron Collider. Under the assumption of a QCD-like hidden sector, hadronic
jets containing stable dark bound states could manifest in proton-proton
collisions. We present a simplified model with a $Z'$ boson yielding the
production of jets made up of dark bound states and subsequently leading to the
decays of those that are unstable to $\tau$ leptons and Standard Model quarks.
The resulting signature is characterised by non-isolated $\tau$ lepton pairs
inside semi-visible jets. We estimate the constraints on our model from
existing CMS and ATLAS analyses. We propose a set of variables that leverage
the leptonic content of the jet and exploit them in a supervised jet tagger to
enhance the signal-to-background separation. Furthermore, we discuss the
performance and limitations of current triggers for accessing sub-TeV $Z'$
masses, as well as possible strategies that can be adopted by experiments to
access such low mass regions. We estimate that with the currently available
triggers, a high mass search can claim a $5 \sigma$ discovery (exclusion) of
the $Z'$ boson with a mass up to 4.5TeV (5.5TeV) with the full Run2 data of the
LHC when the fraction of unstable dark hadrons decaying to $\tau$ lepton pairs
is around $50\%$, and with a coupling of the $Z'$ to right-handed up-type
quarks of 0.25. Furthermore, we show that, with new trigger strategies for
Run3, it may be possible to access $Z'$ masses down to 700 GeV, for which the
event topology is still composed of two resolved semi-visible jets.
