  We demonstrate how to systematically test a well-motivated mechanism for
neutrino mass generation (Type-II seesaw) at the LHC, in which a Higgs triplet
is introduced. In the optimistic scenarios with a small Higgs triplet vacuum
expectation value vd < 10^{-4} GeV, one can look for clean signals of lepton
number violation in the decays of doubly charged and singly charged Higgs
bosons to distinguish the Normal Hierarchy (NH), the Inverted Hierarchy (IH)
and the Quasi-Degenerate (QD) spectrum for the light neutrino masses. The
observation of either H+ --> tau+ nubar or H+ --> e+ nubar will be particularly
robust for the spectrum test since they are independent of the unknown Majorana
phases. The H++ decays moderately depend on a Majorana phase Phi2 in the NH,
but sensitively depend on Phi1 in the IH. In a less favorable scenario vd > 2
10^{-4} GeV, when the leptonic channels are suppressed, one needs to observe
the decays H+ --> W+ H_1 and H+ --> t bbar to confirm the triplet-doublet
mixing which in turn implies the existence of the same gauge-invariant
interaction between the lepton doublet and the Higgs triplet responsible for
the neutrino mass generation. In the most optimistic situation, vd approx
10^{-4} GeV, both channels of the lepton pairs and gauge boson pairs may be
available simultaneously. The determination of their relative branching
fractions would give a measurement for the value of vd.
