I stopped at an ATM late at night, once. I observed a car in the lot, several parking spaces away, with two men in it, watching me.
I promptly put the check back in my pocket, picked up the phone in the ATM kiosk and called the cops. Then I waited to see the results. (I was armed.)
Four (4) cars came roaring in from all directions, blocked the car and one officer got out to take an offensive position behind his engine block. I couldn't hear what was being said, but in about 1 minute, all the officers in all 4 cars got out, guns holstered and went over to the suspicious car and started laughing and yucking. One of the responding uniforms came over to me and said it was a plain-clothes stake out I'd blown.
Pops