The Flag of the Romulan Star Empire was the official flag of the Romulan Star Empire. It consisted of the Romulan emblem set to the left inside a yellow triangle that was bordered by green and black stripes on an orange background.
The flag was displayed at the Khitomer Conference in 2293. A banner bearing a different design was hung outside Camp Khitomer as well. (Star Trek VI: The Undiscovered Country)
According to Vice Admiral William Ross, "Koval would like nothing better than to see the Romulan banner waving over Earth." (DS9: "Inter Arma Enim Silent Leges")
By the start of the 25th century, the flag appeared to no longer be in use following the Empire's collapse. The succeeding Romulan Free State instead adopted its own flag. (PIC: "The Star Gazer")