This is a cast iron rectangular number plate as applied to GWR goods stock. It was fitted at the extreme left of the solebars (one on each side).

Plates such as these are often ignored on models of freight stock, especially in the smaller scales. Some plates were indeed fairly unnoticeable, but others were rather distinctive, and can give much personality to model vans and wagons.

The "Not Common User" wording carried on some vans is one example: The RTR maufacturers paint this wording directly on to the vans in question - but in real life it was carried on a plate. With a transfer sheet and a little Plastikard, this is a good way to detail and personalize your freight stock.