When Her Majesty ascended the Throne back in 1952, she became known as ‘Queen Elizabeth II’. However, some of her subjects in Scotland considered her to be Queen Elizabeth I, considering that the original Elizabeth I had never ruled over Scotland. The fact that Her Majesty was considered their second Queen Elizabeth was somewhat unacceptable to many Scots.
In Scotland, we don't have Elizabeth 2R on the postboxes, since they were continually being defaced, vandalized and even blown up with explosives by unhappy people, and now our postboxes just have the crown without the number.