Investigators observe to gather intelligence.
Yelling a child’s name in public when trying to get them off the playground, out of the store, or into the car will identify a family member by name. The same is true for anybody else hailed in this way by the subject. Knowing the person’s name makes it easy to strike-up a conversation about the subject to gather further information.
Parking permits, school stickers, and vacation magnets on the subject’s car, team shirts and other personalized items are a wealth of information to any Investigator who cares to notice. In minutes an Investigator could know the the names of the subject’s kid and school, along with the subject’s favorite beach and what sport he likes. This is excellent life-style data.
Private investigators have a lot of methods to choose from when determining the facts in a case.