Queen Elizabeth started her reign in 1952. You will often see the initial E R (with a crown between the two letters) denoting Elizabeth Regina (regina being latin for Queen) on objects warranting a royal designation. Here we see a post box dating from the reign of her father King George and bearing the insignia G R which stand for Geore Rex; rex of course being latin for king. And so we therefore know that the next iteration will C R for Charles Rex and then after him W R for William Rex and the back to G R when the infant Prince George is King. So this post office will be right back in style in, oh, about 60 years or thereabouts.