Scientists have long recognised that cannibals operated at Goughâ€™s Cave in Somerset, but were unsure whether the practice of eating other people had any symbolic significance.
Reporting in the journal Plos One, researchers say the unusual cuts on a forearm bone are deliberate.
They are not simple butchery markings.
Nor are they teeth marks.
What is more, the zig-zags appear to match designs used on other engraved objects from the same time period.
"The engraved motif on the Gough's Cave bone is similar to engravings observed in other Magdalenian European sites," said Silvia Bello from Londonâ€™s Natural History Museum.
"However, what is exceptional in this case is the choice of raw material (human bone) and the cannibalistic context in which it was produced.
"The sequence of modifications performed on this bone suggests that the engraving was a purposeful component of the cannibalistic practice, rich in symbolic connotations.
"Although in previous analyses we have been able to suggest that cannibalism at Gough's Cave was practiced as a symbolic ritual, this study provides the strongest evidence for this yet."
Gough's Cave is situated in the Cheddar Gorge, a deep limestone canyon on the southern edge of the Mendip Hills.
Palaeo-investigations first started there more than 100 years ago. It is famous for the discovery in 1903 of "Cheddar Man", the complete skeleton of a male individual dating to about 10,000 years ago.
In 2011, Dr Bello and colleagues presented three skull cases that they said could have been used as drinking vessels.
The braincases had been fashioned in such a meticulous way that their use as bowls to hold liquid seemed the only reasonable explanation.
That interpretation looks even more likely now given the latest research.
The forearm comprises two large bones - the radius and the ulna. In this case, it is a radial bone that the scientists have been studying.
It shows signs of being disarticulated, filleted and chewed - but the zig-zags look nothing like the damage you would expect from these actions.
A series of zig-zag marks on a human bone found in a UK cave is evidence of a cannibalistic ritual that took place some 15,000 years ago.