The problem there is, to prevent theft enroute (a very good reason and far more likely threat than a lawful traveler shooting into the crowd), bags containing firearms are explicitly prevented by statute from being marked on the outside as containing a firearm.  Unless it is an obvious rifle case, which goes to the oversize bag pick-up area, the whole point is to make them blend in. 

In fact, some people who travel professionally with expensive camera or computer equipment deliberately travel with a cheap flare gun so they are able to take advantage of another statute and put a real lock on their bag as opposed to leaving it open to baggage handlers with copies of the TSA lock keys.