The family has now hired a contractor to remove the section of concrete.

The slab will then be delivered to the winner of the online auction, who is identified only as "islandoffthecoast."

An active Lutheran, Ms Serio considers the smudge a slightly odd occurrence, rather than a divine sign or miracle.

"There are some people who need this kind of thing to sort of start them on their faith journey. I don't," she said.

"That's why I don't mind parting with it."