Garage code stencil plates were used until the early 1960s, when London Transport decided, sensibly, to paint the codes on permanently, thereby saving a fortune on plates which were frequently "borrowed" by bus-spotters.
This one was used on buses allocated to BOW (BW) garage, a former tram and trolleybus depot.
If you are collecting this item, please pay in cash when you do so. Otherwise, please send a cheque or postal order or use Paypal. Overseas buyers must use Paypal.
I have another of these, so if you need a pair, let me know before buying, and I'll alter the listing to a pair, and adjust the price with a small discount for posting them together.