Bus Spotters!
You've just reminded me! Mrs K & I used to go to Mildenhall Airshow on the local Residents association coach trip. The airshow was full of aircraft spotters, and the coach park was full of bus spotters. Accordin to the coach driver, there were guys there who used to book onto coach tours with the sole intention of bus-ticking.
I don't think that we are having a pop at spotters here, the vast majority of them are perfectly normal. OK, so we may think their chosed hobby is a bit strange but I'm sure that 99% of us collect something, CDs, stamps, beer-mats, or whatever. What we do find hilarious are the activities of the fanatic spotters.
(Now theres a thought - Extreme Plane Spotting!)
Unfortunately, every hobby has its extremists, which tar all the moderates with a bad name. I enjoy birdwatching, but to most people I am instantly labelled a twitcher - hey, I've not done any twitching for about 15 years .
The time to worry is when you find some guy not only taking your reg, but recording the a/c serial number, then unbuttoning the cowlings to record the engine's serial number!