Flag-Waving: Of course, you know this means war.

We're at peace.

I always assume people know this, but then I run into people who don't: when you fly the Philippine Flag upside-down (with the red above the blue, rather than the blue above the red), you're indicating that the Philippines is in a state of war.

Do you know something I don't?

It was something taught to me as a child, along with learning how to hold it, how to fold it, how to present it when hanging from a house, etc. when I was in the Boy Scouts of the Philippines (as a mere cub scout).

And I never realized how alarming it is until someone makes the mistake.

I remember that some people flew the Philippine Flag upside down at some event during my college years in the U.S. and it irked me -- not because someone hadn't done the research on handling a flag of state properly -- but because it seemed like a bad omen. Or maybe someone had declared war an I'd missed it in the newspaper.

I later found out I wasn't the only one; a lot of other folks who knew were antsy and remained so until the error was rectified.

Also, in times of revolution, rebel soldiers identified themselves to one another with patches of the flag shown vertically.

Usage in Fantasy RPGs

Create a similar flag or device that represents a state or a movement. Make sure it looks the same upside-down and rightside-up, except for colors. One is for peace; the other for war.

Create tensions within the state and around the state. Always show the flag at different times (half-mast when someone of importance dies), or at independence / founding day rites. Play up the importance of treating the flag with respect.

And then, when it's time for a campaign shift -- display the flag upside-down. Wait for a while for the players to get it, then if they don't have an NPC point it out. Is it a revolution? A war with a neighboring state? What's going on?

Then have the PCs find out what the rumor mill has and what they should do next.