Last time I checked a firearm was in 94 I think it was. They didn’t tag the outside of the luggage, but there was a bright blaze orange plastic strip that went inside my bag with my gun case.
They still mark the case within your luggage...still bright orange and says, FIREARM - UNLOADED. The TSA guys like it when firearms are declared...it gives them a little change from the normal routine of groping around in everyones undies.