  Many circumstellar discs appear to have misaligned central regions that give
rise to shadows seen in scattered light observations. Small warps ($<20^\circ$
misalignment) are probably more common but are also more difficult to detect
than the large misalignments studied previously. We present the characteristics
of CO emission that may be used to identify a small disc warp, found from
synthetic $^{13}$CO maps of a model misaligned circumbinary disc. The spectra
are not symmetrical, so fitting a Keplerian model is not appropriate and can
hide a warp or lead to spurious features such as spirals appearing in the
residuals. We quantify the observed warp structure by fitting sinusoids to
concentric annuli of the disc. From this we can trace the radial variation of
the peak velocity and of the azimuth of the peak velocity, i.e., the twist. At
near face-on inclinations, these radial profiles reveal the warp structure. The
twist remains detectable at moderate inclinations (${i_{\rm outer~disc}\lesssim
35^{\circ}}$) in the absence of radial flows but the measured inclination must
be accurate to $\lesssim 5^{\circ}$ to allow detection of the radial variation.
The observed twist does not provide a direct measure of the warp structure
because of its dependence on optical depth. The warp causes broad asymmetries
in the channel maps that span several channels and that are distinct from
localised features caused by embedded planets and gravitational instability. We
suspect that kinematic evidence of warps may have been missed and we suggest a
few examples where the data may be revisited.
