Your referring to 'high sign'. It's an important part of tracking. People often disturb things without even thinking about what's above their knees. I've even seen people who break off branches from trees as they walk by and don't even realize they're doing it.

When you're looking for somebody who wants to be found it's way easier. Family can even sometimes tell you what kind of boots they are wearing or if they have any conditions that may effect their pace.