That's incredibly fascinating. Never heard of them either...
My first guess is a bronze age Benchy.
What's a Benchy? It's a little toy boat that 3D printers make to calibrate a printer.
I would imagine people making kilns to fire pottery would need a way to test the ovens to make sure they work properly. Press a design into clay, fire it up for a set period of time, see if the design holds after firing, and break it in half to verify it fired all the way through.