This happened once:
My boys and I were driving around in the middle of nowhere at night on a dirt road/logging trail, when we decided to stop, turn the car and lights off, and smoke in the darkness. When we finished and went to start the car... clickclickclick. Stranded several miles from anywhere. We smoked all night and slept in the car. In the morning, we began walking. Many hours and two small towns later, we found a gas station. We bought some drinks and something to roll on, and went out and chilled next to the pumps. We were smoking the joint, chillin, when this car rolled up and two older, straight dressed men got out. They were talking with us for a couple minutes, we asked them if they wanted to toke and they said no. Before they left, one of them said "Its not a good idea to be smoking cannabis in front of two undercover police officers". We laughed. One of my boys said "If you are an undercover cop, then prove it". Thats when they both took out their badges and identified themselves as state police. We were still blazing a joint at this time mind you, and we just stared at them, in shock. They told us to be careful, got in their car and left. We kept on our journey, walking for another few miles until we contacted a friend to come and get us. I still do not understand that encounter. All I can guess is they had a more important matter to tend to. We were just teenagers, but its the boondocks out here, and in every scenerio like that an arrest is made.