For what it's worth, thepotteries.org website lists a manufacturer named Gater Hall & Co that utilized the initials G H & Co. No idea if this is related to the GH on your plate. The site lists them as operating from c. 1895-1943. Another similar one is listed, Godwin & Hewitt as using the initials G & H H (not sure what the other H is for) with operation dates of c. 1889-1910.