Heavy neutral leptons appear in popular extensions of the SM, in particular in the context of neutrino mass models and leptogenesis. The interpretation of existing experimental data and sensitivity forecasts for proposed experiments both depend on assumptions about their properties, and they can vary by orders of magnitude when these assumptions are modified. This strongly motivates the use of a common set of benchmark models to enable a fair comparison between existing exclusion bounds as well as the discovery proposals of future experiments and searches. We discuss guidelines for the selection of suitable benchmarks that can effectively capture many properties of realistic neutrino mass models within the simple phenomenological model that is commonly used in experimental studies. We in particular focus on two aspects, namely the branching ratios of heavy neutrino decays into different Standard Model flavours and the branching ratio for lepton number violating decays. We also comment on how these observables can be used to discriminate between models in case heavy neutral leptons are discovered, and to ultimately address the question how these particles are related to the origin of the light neutrino masses and matter in the universe.
