When I checked my gun a while back the DL airline agent was honest that she had no idea what an unloaded vs. loaded gun looked liked and that she was taking my word for it that it was unloaded.
She jumped out from behind the counter and escorted me to a door which leads to TSA baggage screening area (she asked me to wait outside and took, the gun, paperwork, etc. to the TSA for inspection which did not make me really happy) She returned a few minutes later that she stood with it (my gun) while the TSA screened it and handed it over to one of the bag guys to be placed on the plane.
Dan