  We present a catalog of early-time (~10^2-10^4s) photometry and polarimetry
of all Gamma-Ray Burst (GRB) optical afterglows observed with RINGO2 imaging
polarimeter on the Liverpool Telescope. For the 19 optical afterglows observed,
the following 9 were bright enough to perform photometry and attempt
polarimetry: GRB 100805A, GRB 101112A, GRB 110205A, GRB 110726A, GRB 120119A,
GRB 120308A, GRB 120311A, GRB 120326A and GRB 120327A. We present
multi-wavelength light curves for these 9 GRBs, together with estimates of
their optical polarization degrees and/or limits. We carry out a thorough
investigation of detection probabilities, instrumental properties and
systematics. Using two independent methods, we confirm previous reports of
significant polarization in GRB 110205A and 120308A, and report new detection
of $P=6^{+3}_{-2}\%$ in GRB101112A. We discuss the results for the sample in
the context of the reverse and forward shock afterglow scenario, and show that
GRBs with detectable optical polarization at early time have clearly
identifiable signatures of reverse-shock emission in their optical light
curves. This supports the idea that GRB ejecta contain large-scale magnetic
fields and highlights the importance of rapid-response polarimetry.
