CUP and ring marks — a form of prehistoric art — have been found on rocks at Luss and many other places in the West of Scotland.
But the last place Helensburgh website designer Jim Chestnut expected to find an example was near Helensburgh Upper Station.
Jim took this photograph when he saw the markings on the top of the wall on the railway bridge opposite the station entrance.
“I’m curious as to why it is there and if there is a meaning to it,” he said.
Former Helensburgh reference librarian Mike Davis, an expert on local architecture, said: “It looks like a modern take on a cup and ring marking. Curious indeed.”
Cup and ring marks, or cup marks alone, have been found throughout Europe and in countries such as Mexico, Brazil, Greece, Israel and India.
They consist of a depression etched into a rock surface, often surrounded by also etched concentric circles, and may have a gutter leading out from the centre.