Here is the Maker's Plate from RM445. New in August 1960, the vehicle had a 25 year run before being withdrawn in March 1985, then sold in August and subsequently scrapped. The plate was always situated above the luggage compartment by where the conductor stood. Here mounted on ash (the popular timber at PRV for the frames of pre-Routemaster buses), I use this as a desk paperweight.
This plate was of a London Transport generic design (following the roundel & typeface inspired by Frank Pick) and standardised across LT's buses including RT's and Routemasters etc.; so the plates looked similar but carried the name of the specific manufacturer that, in the case of the Routemaster, except for a few prototypes, was PRV. I believe the Patent Numbers shown are those of London Transport.
(See here for other PRV Manufacturers Plates)