"The animal may not even have realized," zoo director Pierre Caille told Agence France-Presse. "We quickly brushed the writing away and there was no harm to the animal."
Pictures showing Noelle with the writing clearly visible on her back have surfaced on social media.
Rhinos at the zoo can choose to position themselves against a wall in the enclosure, and visitors can touch the skin on the rhinos' back, the statement said. The "vast majority do it with respect," zoo staff said.
"We believe that being able to approach such an animal raises the emotion of the visitor and allows it to raise awareness not only about diversity, but also to the majesty of the living around us," the statement said.
Caille said he's considering monitoring the rhino area with video surveillance, but told AFP he "doesn't want cameras everywhere."