While they’re busy loading your bike, hop into their driver’s seat. If you’re lucky, maybe they left the keys in the ignition, free car! If not, either surprise the fuck out of them and ask “Where are we going?”, or call the law, or just beat the shit out of them, your choice.
I had my bike stolen and saw someone riding it the next day. I chased him down and grabbed my bike and cops showed up and handled the situation, but it was a dumb idea because I had no idea what state of mind the guy was in and if he was carrying any weapons.
What made you that sure it was yours?
Paint a stripe or two on your crossbar with distinctive colors. Easy to do, easy to notice & document, hard to duplicate, and hard to remove.