Umbridge stared at the decree on the wall, gasping at the connotation. It looked like her writing, it bore her personal seal - but it was NOT one of her decrees!
Furious, she tore it down, rushing to her office where she ordered her assistents to go around town and get every single one of them down. Then she sat down to write the head of the Aurors.
Mr Weasley,
Someone has taken it on themselves to impersonate me and undermine my authority by writing a fake decree in my name! I demand that the Aurors focus on finding this person at once. This is an attack against our entire society.
Dolores Jane Umbrigde, Acting Minister of Magic
After she was finished she wrote a letter going out to all households letting them know that decree number six was a hoax and that the persons responsible were being sought after. How utterly embarrising.