theoretical default depiction
I have finally identified a flag that I’ve been trying to identify for months. I’ve seen it flying from several locations here in Seattle, but haven’t been able to identify it: The flag is white with — as I’ve seen it — a red stripe along the top. It’s called the Companion Flag. The flag is intended to be flown, along with a national flag (hence the name), to emphasize "what people everywhere have in common," according to their web site. The dimensions of the Companion Flag should vary to match the dimensions of whatever other flag it’s flown with. The top stripe should match a color in the other flag.
The organization supporting the adoption of this flag is headquartered in Seattle. On its web page you'll see it used on many locations.
According to their FAQ, the Companion Flag is supposed to represent "common values" of all peoples. By flying it underneath their respective flags, countries (or cities) would then show their sense of sharing these values.
When used with the US flag, the stripe colors are red or blue