  We propose a realistic protocol for the preparation and readout of mechanical
Bell states in an optomechanical system. The proposal relies on parameters
characterizing a photonic crystal cavity mode, coupled to two localized
flexural modes of the structure, but equally applies to other optomechanical
systems in the same parameter range. The nonclassical states are heralded via
optical postselection and revealed in specific interference patterns
characterizing the emission at the cavity frequency.
