The 32-year-old had to be rescued by firefighters and paramedics outside St Thomas' Church on Peter Street at 10am on Sunday (May 4).
He was wearing a mask and was surrounded by placards. He said he was making a peaceful protest against terrorism.
The protestor was given a fixed penalty notice for behaving in a way that may cause alarm or distress to others.
He remained calm while crews from Parr Stocks Road tried to free him.
He was taken to hospital with a piece of wood still attached to the skin between his fingers and was released a few hours later after receiving treatment.
Watch manager John McCormack said: "This was a very unusual incident and our main aim was to free him from the wood.
"He was taken to hospital but his injuries did not seem to be severe."
A church spokesman said: "We can confirm that a member of the public nailed his finger to the notice board outside our church on Sunday morning. This was done in what appears to be a peaceful protest.
"The gentleman was at no time a threat or danger to anyone else but was determined to continue his protest. We would like to thank the emergency services for their skill in dealing with this issue and our thoughts and prayers are with the gentleman concerned."