Ballochmyle Cup and Ring Markings

We were walking along part of the River Ayr Way today, looking for two landmarks. One was the Ballochmyle Viaduct, which we found without too much difficulty and it's very impressive. The other were the cup and ring markings which were well hidden. Eventually, we found them hidden near a gorge.

The markings were carved in Neolithic times (about 5,000 years ago). What do they mean, I wonder?