Suppose a person is praying for parnasah as they drop a coin into a tzedakah box. At that very moment, there is a loud rumble of thunder, even though the weather conditions wouldn't seem to warrant it, and no further thunder is heard.
If someone is praying and something unusual like this happens at a significant moment in their prayers, is it appropriate to interpret the event as a sign from Heaven that the prayer has been heard (or something else)? I am referring to a case where someone has not asked for such a sign, nor were they expecting one, but the circumstances just seem too remarkable to be coincidence.