Police badges are not that hard to come by. That said, it has become much easier to impersonate cops because in most communities you have numerous agencies, many of whom wear tactical kit all of the time, and many of whom are not in any particular uniform. Tacticool clothing, armor carriers, and velcro- on “police” patches are cheap and easy to obtain online. Even body armor can be shipped to many states.
There is no way to know who is and isn’t a cop.