A much smaller sign, slightly altered on one occasion, on the south front may provide an answer.
House / Hotel
This Georgian house was enlarged in the 19th century, possibly when it was converted into a hotel. My guess is it was the hotel owners who added the large sign onto the street façade and this small one, visible from the road leading towards the centre of Richmond from the south.
Location: Petersham Road / Pictures taken on: 21/05/2008