This d20 uses a vigesimal numbering system where a line is 5, a dot is 1, and a fancy symbol is 0. See https://en.wikipedia.org/wiki/Maya_numerals and https://en.wikipedia.org/wiki/Vigesimal
Since it is base 20, a zero symbol and a dot is 20, a zero and two dots is 40, and so on.
The author marked this model as their own original creation.