A court in the western city of Feldkirch in Vorarlberg also handed the 53-year-old a €1,200 fine.
The woman was charged after she criticized a Facebook posting made by a German football club commemorating the liberation of the Auschwitz death camp and paying homage to the victims. In a response, she accused the club of “spreading lies”.
An anonymous internet user tipped off the police, who searched the woman's house and found the sign in the toilet.
It is illegal in Austria to praise the Nazi era or to deny its crimes.
The woman's lawyer described her as a “simple housewife” who had never heard of Austria's Prohibition Act.
The woman, who has not been named, said she regretted the comments she made online, and that she had been misinformed about the Holocaust after watching a TV documentary. She added that the sign in the toilet was “just a joke”.