  The first stars were likely more massive than those forming today and thus
rapidly evolved, exploding as supernovae and enriching the surrounding gas with
their chemical products. In the Local Group, the chemical signature of the
first stars has been identified in the so-called Carbon-Enhanced Metal-Poor
stars (CEMP-no). On the contrary, a similar C-excess was not found in dense
neutral gas traced by high-redshift absorption systems. Here we discuss the
recent discovery of three C-enhanced very metal-poor ([Fe/H]< -2) optically
thick absorbers at redshift z ~ 3-4, reported by (Saccardi et al. 2023). We
show that these absorbers are extra-galactic tracers of the chemical signatures
of the first stars, analogous to the CEMP-no stars observed in the Galactic
halo and ultra-faint dwarf galaxies. Furthermore, by comparing observations
with model predictions we demonstrate that these systems have most likely been
imprinted by first stars exploding as low-energy supernovae, which provided >
50% of the metals in these absorbers
