This is Hawaiian Flag Day. The flag is unexpected, at least to me—it doesn't seem to catch the island flavor or the Pacific/Asian ancestry of many Hawaiians—and it features a British “Union Jack” in one corner!
But in 1816 this flag was commissioned by King Kamehameha the Great to show Hawaii's close ties with Great Britain. The eight red-white-and-blue stripes stand for Hawaii's eight major islands.
This flag represented Hawaii as the flag of the Hawaiian Kingdom, as the Republic of Hawaii, and as the territory of Hawaii. Now it represents the State of Hawaii.