The symbols themselves neatly match the binary representation of 4 bits, so you can look at the numbers and see them as binary numbers in groups of four if you wish.
These would be great hexadecimal symbols for programmers.
I get what the parent is saying, though. It's just binary digits on a weird looking vertical number line. Each part of the "digit" may as well be a zero or a 1, because that's all it represents. Position tells us what the value is, 2^0, 2^1, 2^2, or 2^3, no need for different symbols. And while we're at it, let's write it left-to-right MSB first, because that's how other numbers work, and it fits on a line nicely, like so: 0101.
The symbols themselves neatly match the binary representation of 4 bits, so you can look at the numbers and see them as binary numbers in groups of four if you wish.
These would be great hexadecimal symbols for programmers.