Maybe I'm confused too, but this is the way I'm reading section 328.
It defines "official sign" as being the 7x3 size and design. It then goes on to mandate that this 7x3 official sign be displayed at each station or window where insured deposits are usually and normally received in the principal place of business and in
all the branches (not to include electronic type facilities).
After the mandatory requirements are met in terms of displaying the 7x3 signs at the teller stations there is discretion about placing other signs.
"Additional bank signs or savings association signs may be displayed in other locations
within an insured bank in other sizes, colors, or materials."
"Official signs or signs reflecting variations in size, colors, or materials may be procured by insured banks from commercial suppliers."
This is just my personal opinion and not a legal opinion. It does not necessarily reflect the opinion of my employer.