The crisscrossed pattern, drawn on stone 73,000 years ago, wasn't used as shorthand for #artlovers, but the hashtag-like design may very well have had symbolic intent. The sketch by early humans, unearthed at an archeological dig site in a South African cave, was drawn with a red ochre crayon—and it may be the earliest drawing ever discovered.

Although the crosshatch design is simple, Christopher Henshilwood of the University of Bergen in Norway suspects it was meaningful, especially considering that similar markings have appeared on artifacts from different Stone Age eras and locales. In a study published today in Nature, Henshilwood and colleagues describe the unique characteristics of the newly analyzed artifact. The pattern may be similar to other ancient markings, but its creator made use of a new technique for the era: color drawing.

“They took a piece of ochre, knocked a flake off it to sharpen it and used it as a pencil or crayon on a very smooth surface that was previously a grindstone,” Henshilwood says. The design’s lines end abruptly on the edges of the silcrete stone, suggesting the piece was removed from a larger grindstone and that the original drawing was bigger. Just how big is an open question that might be answered if the rest of the grindstone is found somewhere in the area.

Earlier carvings in Blombos Cave, where the drawing was found, bear the same crosshatch design. The oldest of these carvings dates to 100,000 years ago, some 30,000 years before the red ochre drawing was made. A similar pattern was also found carved into ostrich shells at Klipdrift Shelter, 25 miles from Blombos, and such crisscrossings made by ancient humans have been discovered in multiple regions from Australia to France, Henshilwood says.

“I think what it means at 100,000 years ago might not be the same thing it means at 70,000 years ago. For whatever reason, I’m almost certain that they didn’t make it arbitrarily. Signs would have meant something to people.”

But trying to understand what the ancient symbols meant may be an inscrutable puzzle. “There, I think we’re stumped,” Henshilwood says.

Nevertheless, nearly three decades of excavations in Blombos Cave, situated on the coast of the Indian Ocean 185 miles east of Cape Town, have given us a window into the lives of the Stone Age people who made these symbols. Ten feet of layers there contain artifacts, fireplaces and the leftovers of many ancient dinners. “It’s almost like a time machine,” Henshilwood says.

Blombos’s inhabitants were Homo sapiens who looked much like we do. They lived in groups of perhaps 20 or 30, moved periodically around the region, and even appear to have been in contact with people in other parts of Africa. Thanks to an abundance of food and resources, the people of Blombos seem to have had a relatively easy time making a living, which could have led to leisure time and creative pursuits.

For example, the cave previously yielded a 100,000-year-old toolkit which was used to manufacture ochre-rich paint. The kit includes two abalone shells used to mix ochre powder, seal fat, charcoal and other liquids. One shell even held a brush with paint still visible on the tip after 100,000 years.

“The preservation is as if they were there yesterday,” Henshilwood says. “I don’t know what they were painting, whether they were painting themselves or the cave walls or whatever. We have no evidence of what they were painting, but we do assume they could paint.”

In addition to the paint and the crosshatched carvings—which some researchers believe are decorative rather than symbolic—the cave dwellers also made a fascinating array of jewelry, crafting more than 100 beads covered in ochre that were strung in different patterns and styles.

Rick Potts, director of the Smithsonian National Museum of Natural History’s Human Origins Program who did not participate in the new study, notes that behavior like toolmaking demonstrates that our ancestors had the cognitive and social abilities to impose design on rock and other materials.

“I see this as a wonderful new line of evidence with regard to applying color that’s consistent with the engravings that are known earlier and even the steps in the toolmaking process,” Potts says. “It’s consistent with the ability to modify an object in some way that has a meaningful symbolic value.”

However, while there’s little doubt that the cave’s inhabitants were drawing with ochre, there is some question as to whether the artifact is a “drawing” in the artistic sense.

“What pops into my mind when we call this a drawing is, ‘a drawing of what?’” Potts says. “It’s a clear demonstration of the ability to produce graphic design. But we usually think of even abstract art as representing something in the outside world. It’s hard to know what the meaning of this design is to the individual who made it.”

Potts suggests the mark might be one of personal possession, for example, labeling the grindstone as the property of an individual or group. “It has been assigned meaning. It’s symbolic in that sense. But is it evidence of the kind of complicated processes of drawing, let’s say, an animal on a cave wall that tells a story?” he asks. “It’s 30,000 years older than the techniques expressed at Chauvet Cave and other places, but it’s not necessarily the same thing.”

Henshilwood agrees that the prehistoric hashtag isn’t figurative art comparable to later depictions painted on cave walls. Rather, he sees the abstract markings as evidence of ancient humans sharing emotions or thoughts. Such a drawing likely sent a message to others, he says, even though we can’t decipher it today.

In some ways, it may be analogous to a souvenir pebble picked up on a trip to the seashore. “You look at it a year later, and the pebble isn’t a pebble, it’s a memory of Scarborough Beach," Henshilwood says. "To you it has an inherent meaning. To anyone else it doesn’t mean anything—it’s a stone. It’s maybe the same kind of thing.”

In the end, it may not matter that we cannot interpret the markings exactly as they were intended. Instead, the artifact is significant simply because it meant something—community, spirituality, don’t touch my grindstone.

“You build meaning into something and you share that meaning with your family or your group, and then over time the meaning gets lost,” Henshilwood says. “I’m not saying that is definitely the reason for this drawing, but I think it’s an interesting possibility."