The tag goes on the OUTSIDE of your locked gun case that is then placed INSIDE your checked bag. Never use a TSA lock to secure your hard-sided gun case. Use a lock or combo lock which only YOU can open. Print out and carry the rules with you. When I first started flying with my ccw, I let an airline clerk talk me into putting the declaration tag inside the COM safe inside the checked bag. It caused me a headache at DTW that took several minutes to get straightened out with TSA and the Detroit PD. It all ended well, and got on my flight OK, but it was completely avoidable.

I now show the clerk the printed rules, and ask to use their airline logo tape. Look for it when you check-in. It's usually at every station. I tape the declaration card to the outside of my safe, and tape around the COM safe. It looks "official", and I have never had a problem since I started doing this.