I wouldn't even quote myself on this matter, but I seem to recall that American workers (perhaps through their unions???) had those billboards put up as a protest against the "invasion" of foreign exports that they felt were destroying American businesses and thus American jobs. They apparently didn't take into account or were ignorant of the fact that several federal administrations (I won't mention a party, but think trunk) had actively encouraged American businesses to send manufacturing jobs overseas. Not living in that part of the country, I'm not sure whether the billboards depicted in the NEC route still exist, but large American flags are frequently displayed at construction sites all over the country ... as though a great deal of the work weren't being done by recent (and possibly illegal) immigrants.
What I've already written should get me into enough doo-doo to last a while, so I'll shut up now. No--one last comment: we Americans do seem much more likely to display our national flag than do the citizens of other countries. In Italy, for example, where I also live, the national flag can be seen flying on some government buildings, but is not typically displayed by homeowners, businesses, local governments, etc.
