It could be that you're walking down the street minding your own business. Police drive by. They stop you and ask you who you are, where you're going, what you're doing, why you're doing it. They want your ID and they're taking notes the whole time. They call it “208” in Toronto and the cards get filed away somewhere in a database that they had this interaction with you.
The part that I emphasize is it's not because they're investigating a crime, not because you're a person of interest; it's because you are living your life freely and here comes a police officer, who has all of the accessories that we know they have, who stands a particular way, who is armed, and then the question is, “Are you not going to answer these questions?” Then the question becomes, “Why aren't you answering my questions? Do you have something to hide?”