Re flags: quite agree with the safety points raised here.
However, several years ago I rode abroad with a mixed bunch who all flew their own national flags from the rear of their bikes.
I did not fly one because, at the time, I thought it smacked of some kind of invasion force out to occupy a foreign country. Admittedly there were only 4 or 5 of us, so well outnumbered!
Flags of one colour, I have no problems with.
Just a personal thing. I respect the countries that welcome me and my bike. And I respect their flags.
A personal thing, as I said.
Perhaps I'm showing my imperialist roots?