We analyze the thermoelectric response in layered metals with spontaneously broken rotation symmetry. We identify the anisotropy of the quasiparticle Nernst signal as an extremely sensitive probe of Fermi-surface distortions characteristic of the ordered state. This is due to a subtle interplay of different transport anisotropies, which become additionally enhanced near Van Hove singularities. Applied to recent experiments, our results reinforce the proposal that the underdoped cuprate superconductor YBa2 Cu3 O6+δ displays such "electron-nematic" order in the pseudogap regime.