Looking for signals in shampoo and conditioner

There’s endless talk about “norms,” but how do we know one exists when it hasn’t been written down anywhere? That’s the question behind this entertaining episode of Shampoo, Property Rights, and Civilization from EconTalk—a sharp, practical exploration of why it’s perfectly acceptable to take the mini shampoo bottles from your hotel room, but not the towels… and certainly not the mattress.

Since such things resist a written format, how do people find out what the current norms entail? Also of interest is to pick up signals when a well-established and purposeful norm is eroding.