  The Majorana nature of neutrinos can be experimentally verified only via {\it
lepton-number} violating processes involving charged leptons. We study 36
lepton-number violating ($\lv$) processes from the decays of tau leptons and
pseudoscalar mesons. These decays are absent in the Standard Model but, in
presence of Majorana neutrinos in the mass range $\sim 100 \mev$ to $5 \gev$,
the rates for these processes would be enhanced due to their resonant
contribution. We calculate the transition rates and branching fractions and
compare them to the current bounds from direct experimental searches for
$\dl=2$ tau and rare meson decays. The experimental non-observation of such
$\lv$ processes places stringent bounds on the Majorana neutrino mass and
mixing and we summarize the existing limits. We also extend the search to
hadron collider experiments. We find that, at the Tevatron with $8 {fb}^{-1}$
integrated luminosity, there could be $2\sigma$ ($5\sigma$) sensitivity for
resonant production of a Majorana neutrino in the $\mu^\pm \mu^\pm$ modes in
the mass range of $\sim 10 - 180 {\gev} (10 - 120 {\gev})$. This reach can be
extended to $\sim 10 - 375 {\gev} (10 - 250 mbox{\gev})$ at the LHC of 14 TeV
with $100 {fb}^{-1}$. The production cross section at the LHC of 10 TeV is also
presented for comparison. We study the $\mu^\pm e^\pm$ modes as well and find
that the signal could be large enough even taking into account the current
bound from neutrinoless double-beta decay. The signal from the gauge boson
fusion channel $W^+ W^+\to \ell^+_1 \ell^+_2$ at the LHC is found to be very
weak given the rather small mixing parameters. We comment on the search
strategy when a $\tau$ lepton is involved in the final state.
