The three vowel diacritics Fatha, Kasrah, Dammah are written doubled , The double vowel-marks are called Tanveen,in Easy word Two Fathah, two Kasrah and Two dammah are known as Tanween. The Tanveen (Two Fatha,Two Kasrah, Two Dammah )give the sound of Noon ( In English sam as the “n” sound). The signs indicate : “an” “in” “un”