Could we not have used braille patterns? Start on a random one and you can just replace the character with the next one so it is possible for the user to see something was entered, but password length isn't given to someone looking over the user's shoulder?

⣾, ⣽, ⣻, ⢿, ⡿, ⣟, ⣯, ⣷

That seems like it would be hard to see, even for the person sitting right in front of it.

why can't they just look at the keyboard...