The finger or toe was found about midday on December 23 and police have had it examined by a forensic pathologist confirming it is human.
"The injury would appear to have been caused by a rock or something similar while possibly swimming or diving," police said.
Since the posting, the owner of the finger has come forward, but not before some hilarious comments from members of the public.
North Sydney Police Chief Inspector Dean Lindley told Mosman Daily the partially severed digit was "very strange".
A beachgoer found the appendage in the toilet block and handed it into police.
"It's not often you get body parts handed in off the street," Inspector Lindley said.