What is an "Air Marshal" and how can I tell if there is one on my flight?

What is an "Air Marshal" and how can I tell if there is one on my flight?

Nico Melendez (TSA Regional Spokesperson) gives expert video advice on: Why do I have to set aside electronic equipment like my laptop and PDA?; What is the best way to travel with camera and film equipment?; What can I do if I feel a TSA employee has treated me inappropriately? and more...