If you know where to look (information gained from an app or website), you can see many satellites either naked-eye or with binoculars (first hand information). That's all I meant by my reply. I am sympathetic to your observation that "being able to see some object move across the sky wouldn't prove anything" however. Such observations are always subject to "maybe it was something else" objections, which are difficult to adequately refute. I think the best object for these types of observation is the ISS, which has very well publicized orbits and a distinctive shape. Observers at locations remote from each other can observe lunar or solar transits, as you mention, and from their observations one can calculate the object's altitude from the relative angels. These calculations place the object at higher altitudes than any airplane has ever been able to fly. Add to that the ability of a good telescope to resolve the object in sharp enough detail to make it obvious that whatever it is, it isn't an airworthy machine for atmospheric flight, hence NOT an airplane. Even the easier observation of the simple "fast dot in the sky" variety are easy to show as not being aircraft. Observers in two cities both watch the dot moving across their sky, simultaneously, exactly where the app predicted it would be. Calculate where an airplane would have to be for both observers to see it, and how fast it would be going. The numbers will be impossible for any airplane ever built.