Copper "traces" as markings?

I’m designing a tiny board, which hasn’t much room for silkscreen markings (at least I can’t fit them with the minimal 0.8mm height the manufacturer requires).
I did found this project though:
https://europe1.discourse-cdn.com/arduino/original/4X/d/e/c/dec5610dcff61ebdb7c199993abe71946387359c.jpeg
I looks like numbers on the inner PTH are made of copper “traces” instead, which can follow the much narrower measurements of the traces.
I could find hints how to make those. My guess it, they weren’t “draw” using the trace tool?
So what is the trick here?

As so often: “Just look at your tool!” (there is a text tool in the PCB editor).
Sorry for bothering.

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