John, . . . if you had a mother like mine, . . . you would remember that you were "caught" many times when you thought you had "gotten off clean".
Reason?? There are subtle clues sometimes, . . . and not so subtle other times, . . . if you have any children, you have observed them in the child's behavior.
Most "guilty" folks cannot ice their emotions well enough to get away with what they are doing, . . . they laugh too much, look away when you talk to them, won't make eye contact as you pass by, try to totally ignore you, duck into another room (or door way, or alley way, etc.), seem nervous in your presence, etc.
And then again, . . . it is absolutely forbidden, verboten, and not legally used, but if anyone thinks for a minute that most police officers do not "profile" people they observe, . . . well, . . . you get to think about it again. It's done, sometimes fully intentionally, . . . sometimes almost unconciously, . . . but it is done. And it works!!
As an example: a newbie to CCW, . . . he'll be wearing a polo shirt or a long tailed shirt out over his pants, . . . in Ohio, he'll slow down as he enters a building (looking for "NO GUN" signs), . . . and he'll invariably (almost unconciously) reach around from time to time and tug down on his shirt tail to be sure his piece is covered. He will not bend over, . . . he'll squat down to see something low or to pick up something off a lower shelf, . . . and from time to time, you will see his elbow on his strong side mash in against his side as he "touches" the weapon to make sure it hasn't moved.
In this profile, . . . you ignore guys wearing shirts tucked in, or wearing short tailed wife beaters, or any shirt where you can see their belt or belt loops. You also can mostly dismiss those wearing sweats, upper and lower, especially if the sweatshirt is tucked into the sweatpants.
Smelling trouble as an LEO is no different than smelling trouble as a mechanic on an assembly line. There are "signs", "sounds", and "events" that precede trouble, . . . LEOs have developed the senses to understand these events in the same way doctors diagnose diseases, or mechanics diagnose trouble in your car's engine.
Quite honestly, . . . I have developed a couple of profiles on my own, . . . for people who I may meet, . . . wherever I may be, . . . and the more "dots" I connect on an individual person, . . . the closer I watch them, whether it be in Wally World, . . . or in my church. Oh, . . . and no, . . . I won't share, . . . they are indigent to the population and presence of where I live, . . . and probably would not be as useful to you in your location. But you have the same opportunity wherever you live to develop your own "profiles" and to be watchful/observant for them.
May God bless,
Dwight