An object with a message (such as "you are here") on it is known as a sign.  Since the sign is located over the building's doorway, it is reasonable to assume that it is the building's sign.  Wording on signs is generally upright; therefore, if the message on the sign is upside down, the sign itself is most likely upside down.


Consider the statement "A building says "you are here" upside down over it's doorway.". Based on this "The building's sign is upside down." a true statement? Yes, no, or I don't know?