Can the term be お姉さんbe used to address female strangers politely?
It is customary in Japan to address people unknown to you by the respectful,term for the position they would appear to hold in their own family - おじいさん , "grandad", for an elderly man, おばあさん, "granny", for an elderly woman, おくさん, "married woman" for a woman who would appear to be, say, over thirty-five. Not all relationship terms are used like this: おかあさん , "mother", and おとうさん, "father", for example. Also, the age, sex, etc of the speaker affects usage: a young woman might address a middle-aged man as おじさん , "uncle", but I don't think a male of any age would. (I remember the shock I felt the first time a young woman addressed me as おじさん.) おねえさん , "older sister", can be used to address a woman in late teens to early twenties. It is, for example, (or used to be)used to attract the attention of wait-staff in a cafe or restaurant. But all these need to be used with caution. To attract the attention of a young woman who, for example, has dropped something in the street in front of you, it's probably best to use おじょうさん, a respectful word for daughter or young woman. Take care. You can sound very presumptuous if you get it wrong.