What makes the flag of the Philippines unique?

Well, according to Wikipedia...

"The Philippine flag is unique in that it can indicate a state of war. When the flag is upside-down such that the red is on top (or the red is at the left when displayed vertically), it means that the Philippines is at war."

https://en.wikipedia.org/wiki/Philippine_flag

The Philippine flag is unique in that it can indicate a state of war. When the red field is displayed on top (or the left hand side of the observer when the flag is displayed vertically), it means that the Philippines is at war. This was first flown on February 4, 1899, at the start of the hostilities of the 1899-1913 Philippine-American War. It was last officially ordered flown with the red stripe up, in December, 1941, following the Japanese attack on the Philippines on December 8, 1941. It remained flown with the red stripe up by the government of the Commonwealth of the Philippines, both during the Japanese invasion and subsequently in front of the temporary capital of the Commonwealth government-in-exile, which was located in the Philippine Resident Commissioner's building in Washington, D.C. The Japanese-sponsored Second Republic of the Philippines flew the flag with the blue stripe up from its proclamation in 1943 until President Jose P. Laurel proclaimed the existence of a state of war with the Allied powers in 1944. There was also a brief attempt to restore the pre-1937 proportions but this wasn't successful. Today the provinces of Basilan and Zamboanga Sigbuhay flow their flags upside down since 2001.

Removed dead link. Link to Wikipedia page in other response is valid to confirm this information as well.