Is it illegal to sing on a public train?

It depends on the specific jurisdiction and the rules of the public transit system in question. In general, singing on a public train is not considered illegal in most places. However, if the singing is disruptive to other passengers or violates any specific regulations, it could potentially be considered a violation of the law. For example, if a person is singing loudly and causing a disturbance, they may be asked to stop by the train operator or law enforcement. Additionally, if a person is using a musical instrument or amplified speakers without permission, they may be in violation of noise or public disturbance laws.