Although all my accounts are in USD or EUR, all my reminders under bills & income show up in British pounds.
As far as I can determine … If your computer is set to British language settings it simply replaces the $ sign with the £ sign … and all amounts in the Bills & Income reminders dialogs appear to use a hard-coded $xxx.xx numeric edit format, ignoring the actual reminder's currency.
I have a few reminders which execute in € - accounts and should show amounts as, e.g., €10.00 … but, no, they show $10.00
Problem solved! Thank you.