  The halo assembly bias, a phenomenon referring to dependencies of the
large-scale bias of a dark matter halo other than its mass, is a fundamental
property of the standard cosmological model. First discovered in 2005 from the
Millennium Run simulation, it has been proven very difficult to be detected
observationally, with only a few convincing claims of detection so far. The
main obstacle lies in finding an accurate proxy of the halo formation time. In
this study, by utilizing a constrained simulation that can faithfully reproduce
the observed structures larger than $2\,$Mpc in the local universe, for a
sample of 634 massive clusters at $z\le 0.12$, we find their counterpart halos
in the simulation and use the mass growth history of the matched halos to
estimate the formation time of the observed clusters. This allows us to
construct a pair of early- and late-forming clusters, with similar mass as
measured via weak gravitational lensing, and large-scale bias differing at
$\approx 3\sigma$ level, suggestive of the signature of assembly bias, which is
further corroborated by the properties of cluster galaxies, including the
brightest cluster galaxy, and the spatial distribution and number of member
galaxies. Our study paves a way to further detect assembly bias based on
cluster samples constructed purely on observed quantities.
