Earlier this year I was flying SEA-DFW and waited by the gate as 2 uniformed MPs came up to the gate desk with 3 young men. The young guys were dressed in street clothes and actually carried their own little backpacks. No handcuffs. The 3 and 1 MP stood to the side as the other MP talked to the GA. He showed her some official looking paperwork. They were allowed to board first and were escorted by the GA. Few minutes later the GA came back and as the rest of us were getting to board one of the passengers asked the GA about this. She said that the 3 kids changed their minds and decided not to report after signing up. She said that she has seen this happen more and more lately.
I always wondered what the punishment for something like this would be. The kids did not look very happy.