Right-The Flag.
I'm still unclear on why the OP thinks a Flag is a bad idea?
He has been told by many many drivers that he is hard to see,
But he insists that since they eventually see him well enough to yell at him -that he is visible enough.
He isn't an idiot-so he knows that those drivers were telling him " I barely saw you" or "I saw you at the last second " and
"I almost ran you over because you are below my usual sight line"
What kind of instructor doesn't understand what those drivers are trying to tell him??
You imply-but don't say-that a flag won't make your bike more noticeable??
Predators-us-notice change in movement .A flag wobbling around in drivers sight lines will attract their attention.Part of the justification of the "take the lane" is to make yourself more visible.
Heck with cell phones and texting we need it.
Cop had a point.