The sculptures feature the same carved symbol and come with a riddle attached.

Despite CCTV film showing a man leaving three heads outside a post office, their origin remains unknown.

So far, 12 have appeared in Goathland and Kilburn, North Yorkshire; four in Arthington, West Yorkshire and three in Braithwell in South Yorkshire.

Each of the heads, which are up to a foot tall, looks different but all feature the same carving - which appears to spell out the word "paradox" - and a note bearing the riddle: "Twinkle twinkle like a star does love blaze less from afar?"

The villages they have been found in are up to 50 miles from each other.

Mike and Valerie Hoyes, who run a post office in Braithwell, found three heads outside their business on the morning of 23 August.

We would love to meet or find out who it is, whoever it is is extremely talented

Fiona Gould, owner of the Forresters Arms Hotel, Kilburn

Checking their CCTV footage, they discovered a man they did not know dropping off the stones in a small car at around 0400 BST. They have since given the tape to the police.

Mrs Hoyes said: "It's very weird.

"They're a bit like gargoyles really, obviously somebody has taken a lot of trouble if they have been carved.

"On the back it looks like an occult thing, it does actually spell paradox, but we don't know what any of it means."

The heads have been found in villages 50 miles apart

After speaking to friends and neighbours he became aware of two more of the sculptures being left in the village.

Stonemasons quizzed

He contacted stonemasons at York Minster in an effort to trace what appeared to be a mason's mark on his heads but said nobody had ever seen anything like it before.

He also turned to the internet and dictionaries to try to find out details about the rhyme but again drew a blank.

Mr Griffiths said: "I think it's a publicity stunt - I can't see anything else.

"They're not sinister or anything like that, it's just a puzzle. We're all just waiting and wondering to find out more."

Fiona Gould, the owner of the Forresters Arms Hotel in Kilburn, received her head last month.

She said: "He turned up a week last Monday between 1.30am and 7.30am. I opened the door and there he was, as large as life, sat on the patio."

She discovered that five more heads had appeared in Kilburn and another six in nearby Goathland.

Miss Gould's head now has pride of place on the bar in her pub.

"We would love to meet or find out who it is, whoever it is is extremely talented," she added.