  Marked correlation functions, which are sensitive to the clustering of
galaxies in different environments, have been proposed as constraints on
modified gravity models. We present measurements of the marked correlation
functions of galaxies in redshift space using 361,761 LOWZ ($z_{\rm eff} =
0.32$) galaxies from the Sloan Digital Sky Survey III (SDSS III) Baryon
Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) and compare them
to $\Lambda$CDM+General Relativity simulations. We apply mass cuts to find the
best match between the redshift space autocorrelation function of subhaloes in
the simulation and in the observations. We then compare the marked correlation
functions, finding no significant evidence for deviations of the marked
correlation functions of LOWZ galaxies from $\Lambda$CDM on scales $6 \
h^{-1}$Mpc $ \leq s \leq$ $69 \ h^{-1}$Mpc. The constraining power of marked
correlation functions in our analysis is limited by our ability to model the
autocorrelation function of galaxies on small scales including the effect of
redshift distortions. The statistical errors are well below the differences
seen between marked correlation functions of $f$(R) gravity models and
$\Lambda$CDM in recent publications (Armijo et al., Hern\'{a}ndez-Aguayo et
al.) indicating that improved future theoretical analyses should be able to
rule out some models definitively.
