We examine the observability of heavy neutrino signatures at the LHC. As a reference model, we consider a U(1)' enlarged Standard Model (SM) encompassing three heavy Majorana neutrinos alongside the known light neutrino states. We show that, in some regions of the parameter space, heavy neutrinos can be rather long-lived particles producing distinctive displaced vertices that can be accessed in the CERN LHC detectors through the exotic SM Higgs decay. We also exploit the theoretical decay via heavy (non-SM-like) Higgs boson and Z' production ultimately yielding semileptonic signatures of short-lived heavy neutrinos. Depending upon how boosted the final state objects are, we define different possible selections aimed at improving the signal to background ratio in LHC Run 2 data.