  We investigate the frequency of high carbon-to-oxygen (C/O $= 0.9$) M dwarf
stars in the solar neighbourhood. Using synthetic spectra, we find that such M
dwarfs would have weaker TiO bands relative to hydride features. Similar
weakening has already been detected in M-subdwarf (sdM) stars. By comparing to
existing spectroscopic surveys of nearby stars, we show that less than one
percent of nearby stars have high carbon-to-oxygen ratios. This limit does not
include stars with C/O$=0.9$, [m/H]$>0.3$, and [C/Fe]$>0.1$, which we predict
to have low-resolution optical spectra similar to solar metallicity M dwarfs.
