The baggage label, with my ticket code was entered into the computer as containing a declared firearm. Even the lady at the boarding gate at my home airport, who had never seen my bag, knew from the ticket code that my checked bag contained a firearm. She mistakenly mentioned it out loud to me at the gate. Anyone scanning the code on the tag knows there is a firearm inside.
While there is no label advertising to the general public that a firearm is inside, from a standpoint of anyone hooked-up to the baggage handling computers, the suitcase is in fact clearly labeled. To the TSA and the airline, it is indeed clearly indicated that a firearm is inside.