Does the second floor have the right to stop the plaque from hanging on the first floor?

Not necessarily. If the rights and interests of the second floor are infringed, it has the right to stop it.

If the plaque hanging on the first floor affects public safety and hygiene, then the second floor has the right to stop it. If the plaque hanging on the first floor infringes the legitimate rights and interests of the owners on the second floor, such as affecting the lighting and ventilation on the second floor, then the second floor also has the right to stop it. Finally, if the plaque hanging on the first floor is supported and recognized by the property and related management departments, then the second floor may not be able to stop it.