The sign was posted in Manly library in Sydney over the weekend.
All non-fiction books by the cyclist, including “Lance Armstrong: Images of a Champion”, would soon be moved to the fiction section, it read.
A council spokesman said the sign was a joke and that local libraries could not arbitrarily reclassify books.
Last week Lance Armstrong ended years of denial by admitting he used performance-enhancing drugs during all seven of his Tour de France wins.
The 41-year-old confessed during an interview with chat show host Oprah Winfrey that was watched around the world.
“This was a prank, it happened on Saturday and a member of the public has taken a photo and posted it on social media and it’s gone viral on social media,” said Chris Parsons of Manly Council.
“However you can’t simple reclassify books from fiction to non-fiction,” he said, explaining that classifications were decided at a central level.
Local reports said the sign was posted by a student working part-time in the library. Mr Parsons did not confirm this but said a “little review” would take place at the library.
“It’s a big, busy library and someone has played a practical joke - it’s gone unnoticed for a while and once staff noticed they changed it,” he said.
Pictures of the sign - which ends with a smiley face - have been widely circulated on social media, with many commentators congratulating the library on its stance.
“Librarians do have a sense of humour,” said one Twitter user. “Awesome. Slow clap Manly Beach Library,” said another.




