Open up; Police!

Would you open your door to a stranger? Probably not.

Would you open your door to a stranger in a police uniform? I hope not, because it just got you shot in the chest.

It's very simple, identify the people through a window or peephole, and when they indicate or imply they are law enforcement officers, ask them which department, and then call that department with 411 to confirm they are who they say they are. Ask for badge numbers and last names, and confirm with the station. Use 411 or your yellow pages, don't call a number they give.

It's not something a lot of people think about (myself included up until a few years ago), but it's a safety thing. If the cops get indignant, tell them to fuck off, and call 911. Seriously.

While we're talking about people in uniforms, you know what happened when a bunch of fed ex uniforms went up on ebay? They sold out instantly. This is why you should have a handgun on your person when answering the door when you are not expecting visitors.