ARE SHEEP MARKED TO PREVENT RUSTLING?

ARE SHEEP MARKED TO PREVENT RUSTLING? I was interested in the article about sheep rustling in part because when we were in Ireland we saw sheep marked with large blotches of primary colors, and we were told that the markings showed ownership. Would the markings deter rustling? This series of answers on Yahoo Answers was very informative, and one answer seems to suggest that the markings may help on rustling, but obviously the markings are unable to stop the current wave of rustling, perhaps because the markings don’t provide a way to trace a lamb back to its owner. I had formed the impression when I was in Ireland that the markings were partly intended to prevent not the rustling of sheep but rather the stealing of grass by somebody else’s sheep.