Jumpseat
This is all a bit silly boys. If the bad DOTARS man sees you sitting on the jumpseat, provided you have your ID, you are fine. The bad DOTARS man has no idea if you are on duty travel or not. He doesnt get a copy of your rosters.
Advice: If the DOTARS man askes you if you are on duty travel, answer YES!
As long as you look the part, they wont bother you. we've been doing it this way for years, and will keep doing it this way for years to come.