To sing in a dream is a good omen, as it symbolizes happiness, luck and success. The dream shows that you make other people happy while entertaining them with your good mood and vibe. If somebody else sang in a dream, then it also means that you feel that you live in a harmony, happy and peaceful atmosphere, where everyone is sharing joy with each other. Alternatively, the dream could predict about unpleasant feelings such as sadness, but only in those cases when the one is singing or hears somebody singing very sad songs.
Read more about dreaming of Singing in other dream meanings interpretations.