  Unconventional responses upon breaking discrete or crystal symmetries open
avenues for exploring emergent physical systems and materials. By breaking
inversion symmetry, a nonlinear Hall signal can be observed, even in the
presence of time-reversal symmetry, quite different from the conventional Hall
effects. Low-symmetry two-dimensional materials are promising candidates for
the nonlinear Hall effect, but it is less known when a strong nonlinear Hall
signal can be measured, in particular, its connections with the band-structure
properties. By using model analysis, we find prominent nonlinear Hall signals
near tilted band anticrossings and band inversions. These band signatures can
be used to explain the strong nonlinear Hall effect in the recent experiments
on two-dimensional WTe$_{2}$. This Letter will be instructive not only for
analyzing the transport signatures of the nonlinear Hall effect but also for
exploring unconventional responses in emergent materials.
