Residents of Yorkshire could be forgiven for wondering if Easter Island has come to the North of England after at least 19 carved stone heads were left on doorsteps across the county.

The sculptures are all slightly different but each bears a carved symbol which appears to spell out the word “paradox” and comes with a riddle attached. They were left at dead of night outside businesses and homes in four places.

Recipients have been unable to decipher the riddle: “Twinkle twinkle like a star, does love blaze less from afar?” A publicity stunt is suspected, but for what remains unknown.

Mike and Valerie Hoyes, who run a post office in Braithwell, near Rotherham, South Yorkshire, found three heads outside their shop one morning in August.

Checking their CCTV footage, they found images of an unknown man dropping off the sculptures at around 4am. “It’s very weird,” Mrs Hoyes said. “They are a bit like gargoyles; obviously somebody has taken a lot of trouble if they have been carved. On the back it looks like an occult thing, but we don’t know what any of it means.”

George Griffiths, an artist from Arthington, near Leeds, found a head on his doorstep one morning. Another appeared two weeks later. Finding that two more had been left at other addresses in his village, he sought advice from stonemasons at York Minster in the hope that they might be able to decipher what looked like a mason’s mark on the head. But they had no idea what it meant. Mr Griffiths searched dictionaries and the internet to trace some meaning to the rhyme, but drew a blank.

“I thought somebody had just dumped it, that it had fallen off the back of a lorry,” he said.

“But then I read the message and thought, it’s queer, this is. I think it’s a publicity stunt; I can’t see anything else.”

Fiona Gould, owner of the Forrester Arms Hotel in Kilburn, North Yorkshire, received her head last month. “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.”

The sculpture now has pride of place in the hotel bar. “We would love to meet or find out who left it; he is extremely talented.”

Ms Gould discovered that five more heads had appeared in Kilburn, and a further six in the nearby village of Goathland. North Yorkshire police confirmed reports of numerous heads being found, but could shed no light on the mystery.

There are reports of a 20th head being discovered in a village near Selby where the huge parish church exhibits the coat of arms of George Washing-ton’s ancestors, who lived in the area. The arms include three stars and two stripes and what they could have evolved into is somewhat less of a mystery than a sudden outbreak of anonymous stone heads.

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