  We discuss in detail the possibility that the ``type-II majoron'' -- that is,
the pseudo Nambu-Goldstone boson that arises in the context of the type-II
seesaw mechanism if the lepton number is spontaneously broken by an additional
singlet scalar -- account for the dark matter (DM) observed in the universe. We
study the requirements the model's parameters have to fulfill in order to
reproduce the measured DM relic abundance through two possible production
mechanisms in the early universe, freeze-in and misalignment, both during a
standard radiation-dominated era and early matter domination. We then study
possible signals of type-II majoron DM and the present and expected constraints
on the parameter space that can be obtained from cosmological observations,
direct detection experiments, and present and future searches for decaying DM
at neutrino telescopes and cosmic-ray experiments. We find that -- depending on
the majoron mass, the production mechanism, and the vacuum expectation value of
the type-II triplet -- all of the three decay modes (photons, electrons,
neutrinos) of majoron DM particles can yield observable signals at future
indirect searches for DM. Furthermore, in a corner of the parameter space,
detection of majoron DM is possible through electron recoil at running and
future direct detection experiments.
