thank you. Which sources fit into this category?

That's an interesting question, especially today when "fake-news" is not uncommon. Also remember, the Mashiach is not going to do super-natural miracles. He will be a political and military leader in Israel, the Rambam writes, similar to Bar Kochva. In general, a live video film of a professional reporter who has a reputation for honesty who doesn't want to risk harming his name, would be a reputable source to believe. Especially if that sensational story of the Mashiach's coming appears on the various major news networks. Remember, most journalists clearly do not have a religious agenda, so they must be pretty convinced…