Go ahead and report it if you think the people/person/group that receives the complaint will care and then make a change. Security anywhere is not about catching anyone doing something, but to intimidate anyone from wanting to do something. The fact that the bag goes through screening means someone will take the chance of getting caught seriously. But if someone wants to do something, they will figure out a way, and it wont be as simple as trying to use a line where no one really looks. They will put what they need where no one can, or dares, look.