Pseudo Nambu-Goldstone bosons (also known as axion-like particles) with flavour-violating couplings to the Standard Model (SM) fermions are a rather generic consequence of spontaneously-broken global U(1) symmetries, e.g. if the SM fermions carry flavour non-universal charges. A possible consequence is the occurrence of flavour-violating decays of hadrons and leptons into light axion-like particles. These exotic signatures are a powerful probe of such kind of scenarios. I will discuss the phenomenological consequences at future experiments, focusing in particular on searches for lepton flavour violation, and compare their sensitivity to the symmetry-breaking scale with bounds from stellar evolution.