Very similar to a hodown, only involving police. If one is spotted, the observer should yell Podown!! Then point and laugh. (because cops, especially in large groups, are a joke.)
This can sometimes be accompanied by rolling down your window and yelling "Suuuueeey!!! Here piggy, piggy, pig!!!"
A group of cop cars chilling in a random parking lot late at night... Definitely a Podown!
5 cop cars roll into the McDonald's parking lot simultaneously... This is most assuredly a podown.