  In recent years an increasing number of observational studies have hinted at
the presence of warps in protoplanetary discs, however a general comprehensive
description of observational diagnostics of warped discs was missing. We
performed a series of 3D SPH hydrodynamic simulations and combined them with 3D
radiative transfer calculations to study the observability of warps in
circumbinary discs, whose plane is misaligned with respect to the orbital plane
of the central binary. Our numerical hydrodynamic simulations confirm previous
analytical results on the dependence of the warp structure on the viscosity and
the initial misalignment between the binary and the disc. To study the
observational signatures of warps we calculate images in the continuum at
near-infrared and sub-millimetre wavelengths and in the pure rotational
transition of CO in the sub-millimetre. Warped circumbinary discs show surface
brightness asymmetry in near-infrared scattered light images as well as in
optically thick gas lines at sub-millimetre wavelengths. The asymmetry is
caused by self-shadowing of the disc by the inner warped regions, thus the
strength of the asymmetry depends on the strength of the warp. The projected
velocity field, derived from line observations, shows characteristic
deviations, twists and a change in the slope of the rotation curve, from that
of an unperturbed disc. In extreme cases even the direction of rotation appears
to change in the disc inwards of a characteristic radius. The strength of the
kinematical signatures of warps decreases with increasing inclination. The
strength of all warp signatures decreases with decreasing viscosity.
