On modern colour notes one conventional way to help the visually impaired is to make the note have a distinctive colour theme. Most countries do this, and I believe the latest US notes finally have at least subtle coloured elements.
[Gets out British "paper" money that hasn't been touched since the lockdown started months ago because who pays cash now?]
As well as being different sizes, my £10 notes are orange, while the £20 is purple. The tenners have this big orange splodge that's actually a book with the initials JA (Jane Austen) and the twenty has a purple splodge whose meaning might be obvious to me if I liked art enough (relating to Turner, a famous British painter).
Comparing sizes is hard to do quickly, whereas you can see instantly if the money you're trying to pay with or receiving in change is the wrong colour.
The vast majority of visually impaired people are not literally blind and that's really important when designing for the general population. If you force everybody whose sight has deteriorated to the point where they can't read text to resort to feeling note sizes you're missing a vast middle ground of people who'd have been served by just choosing a different colour for each denomination.
In australia the new bills do have tactile dots to distinguish them for people living with blindness. About halfway along the bottom of the new 5 you can feel it.
[Gets out British "paper" money that hasn't been touched since the lockdown started months ago because who pays cash now?]
As well as being different sizes, my £10 notes are orange, while the £20 is purple. The tenners have this big orange splodge that's actually a book with the initials JA (Jane Austen) and the twenty has a purple splodge whose meaning might be obvious to me if I liked art enough (relating to Turner, a famous British painter).
Comparing sizes is hard to do quickly, whereas you can see instantly if the money you're trying to pay with or receiving in change is the wrong colour.