The top half of a 2 might kinda look like the curve shape, and the bottom stroke of a 2 looks like a horizontal bar. So if there were partial characters hanging from the central pole, they might look a bit like those...
But… If it’s that, the curve probably only works on the bottom right anyway. So if you’re willing to mirror it for the bottom left, why not mirror to the top too?
And… That doesn’t really explain the 1 parts anyway. They’re just using “whichever part of a 2 isn’t being used for 2”.
Aha. For each side of the pole, you can write the binary representation of 4 bits vertically, and where there’s a 1 you have a line joining it. The middle two bits both go to the middle of the pole, so they have to curve off upward or downward to indicate which they are.
So 2 is 0010, and you have no lines in the top half and one line representing the bottom of the middle, so it curves downward.
Whereas 4 is 0100, so it has the upward-curving middle-connecting line, and none in the bottom half.
There’s a reason for the “wrinkle” :)
The top half of a 2 might kinda look like the curve shape, and the bottom stroke of a 2 looks like a horizontal bar. So if there were partial characters hanging from the central pole, they might look a bit like those...
But… If it’s that, the curve probably only works on the bottom right anyway. So if you’re willing to mirror it for the bottom left, why not mirror to the top too?
And… That doesn’t really explain the 1 parts anyway. They’re just using “whichever part of a 2 isn’t being used for 2”.
So I guess this isn’t a complete explanation.
Nope, not based on the shapes of numerals.
Hint: are you sure it’s base 4?
Aha. For each side of the pole, you can write the binary representation of 4 bits vertically, and where there’s a 1 you have a line joining it. The middle two bits both go to the middle of the pole, so they have to curve off upward or downward to indicate which they are.
So 2 is 0010, and you have no lines in the top half and one line representing the bottom of the middle, so it curves downward.
Whereas 4 is 0100, so it has the upward-curving middle-connecting line, and none in the bottom half.