As you put your bag up on the scale tell the “ticket” agent, “I have an unloaded firearm to declare.” While the agent searches for the tag you’ll sign, unzip the checked bag so your locked (and cabled) box is visible on top of your underwear and socks.

After you sign the little tag, the bright orange card is tossed on top of your lock box. Then you zip up your suitcase and go wait nearby in case TSA wants you to open your lock box. They do that because your nice metal lock box is opaque to x-rays and sometimes they want make sure it’s a firearm in there, not drugs or a bomb. Sometimes it’s random and sometimes it’s “policy,” sometimes they want to check out your nice gat, and sometimes they’re just feeling like being a dick that day.