Generally speaking the signals would be coming from say Analytics for example so based on what’s coming in to Audience Manager (see Signals Dashboard link below), you can catch these as key-value pairs in Audience Manager traits. It could be page views, events, it could be something else you feel is more adequate.
See documentation below to get a better sense of what signals and key-value pairs are and I’d also point out you have the Recency & Frequency feature at segment level, which might also help better define your audiences (eg: <= 2 page views / event in last 30 days)
Key-value pairs explained
Recency & Frequency
Hope it helps!