The police do have a distinct knock. The 35 year old who lives with his mother and can't work due to 'depression'....has been arrested two times in the past few months. When I hear that particular knock, I always know he has stolen yet another person's valuables. To make it worse, he has had garage sales with items probably taken from another part of the city. You can get a good deal on cool stuff if you get their before the police do.