According to Znamierowski, the flag of the Union is 2:3, horizontally divided red-white-green (45:10:45), with a yellow crescent pointing up in the middle of the flag and five white stars placed in an arc of circle above the crescent. The flag was adopted in 1990. Its colours are those of the member countries, which are represented by the five stars. It seems to be evident, although Zanmierowski does not explicitly state it, that the crescent symbolizes Islam, which is the official religion in the five member states. The crescent appears on the flag of Algeria, Tunisia, and Mauritania. This latter country has on its flag a crescent similar to the one shown on the Union flag. I guess this crescent was chosen because Mauritania is the only country of the Union to have a yellow element on its flag.