that looks like and airport sign
if you were at heathrow and started talking about hijacking or bombs you would very quickly have a few men with sub machine guns pointing at you.
there have been quite a few people who when asked abut their luggage in the uk at check-in have made flippant remarks about bombs in there case who seriously wish they hadn't.
there are somethings that freedom of speech and civil liberties have to go out the window. if the safety of 400 passengers is in anyway compromised by the chat of two then in my book the two chatting are delayed and investigated and the 398 go with confidence on their flight.