See I would have opted for a sign that read:

Dear outraged dumb-dumbs,
This is the flag of Norway, not the confederate flag. If you’d ever bothered to open a history book or even pay the slightest amount of attention before becoming outraged, you might know that the latter is known as the “stars and bars” because, not surprisingly, it has stars on it, which the flag of Norway does not, in addition to many other differences. Do the world a favor and educate yourself a tiny bit before opening your mouth again, unless it’s to breathe because let’s be honest here, you’re definitely a mouth-breathing moron.
Sincerely,
Smart people