That's a soup bottle, which is used to wash hands. Hui people have developed a good habit of washing their hands with "soup bottles and soup pots" before and after meals. In front of all Muslim restaurants and food stores, there is a wooden sign with something like a small hip flask painted on it, and two pieces of red cloth, one long and one short, are hung below. The picture above is actually not a hip flask, but a washing kettle, also called a soup bottle.