Yup. Or they think it's like a Triumph. Retro. It aint retro if it's actually just unchanged.
I get the thumbs up too. I remember the very first one on Enfield. Now I "give" the thumbs up to sweet rides. Before I wouldn't because I didn't want people to think I was being a condescending jerk, but now I get it. I know that if I give the thumbs up, the owner of the vehicle will actually get it. So like Youtube, I throw out the thumbs up.
The most common site though, is to look over when at a traffic light and see someone just starring. If they see you see them, you get the nod. We've all gotten the nod. That's sweet. No conversation, just a silent acknowledgment that they-know you-know they-think your ride is sweet.
But man, the "what year," question... Maybe I'll just start answering that with a thumbs up too.