We study the imprint of a coupling of scalar dark energy to a photon on the cosmic microwave background polarization. Both the time-evolving field value and the perturbation of the scalar induce B-mode polarization. For a wide range of scalar dark energy models allowed by current observational data, we conclude that future cosmic microwave background data will find either a cosmic parity violation in a temperature-polarization correlation due to the field value, or perturbation-induced B-mode polarization that is indistinguishable from that generated by primordial gravitational waves.
