Are you talking about the soup bottle? The container of water traditionally used by Muslims during the ablution was later often used on the signboards of halal restaurants as a sign of "halal". As shown in the picture:

As for "Dua", which is often called "Dua Yi", it is the transliteration of the Arabic "prayer/word". China usually uses the Arabic logo (tuam) on the signboard. ?al-islam or al-matuam?al-islamy---Chinese for "halal food"/"halal restaurant") is also called "Dua Yi" or "Jingdu". For example: Grandpa told his little grandson: " Don’t go to a restaurant that doesn’t have “Du A Yi” (Jing Du). ”