The idea is fairly old. I think the first time I heard it was the latter part of the Bush era? Someone told me secondhand about how having a Canadian flag on the backpack makes some airports friendlier. that’s also around when I started traveling internationally for work so it could have been around even earlier than that. I never knew any Americans who actually did it. I did work with a lot of Southerners and we all had distinctively American accents, so I don’t think we could have pulled it off. Maybe a Minnesotan could pass.