Makes me think of the trick we used a large website I used to work for: we'd have everybody and their mother copy our T&S because that was easier that writing it themselves. So we added a 2 very uncommon spelling mistakes into it on purpose. After that just a simple google Alert on those keywords would tell us immediately when someone copied our T&S.

Adding something weird/uncommon can make something easily measurable (as showcased in both my example as the article).