What is it? Where did it come from?

I sometimes start my lessons with a mystery object, and ask the class to come up with some ideas about what it is and how it could be used. This is normally a piece of science apparatus, from the back of the prep room cupboard, that they haven't yet come across. We have a lot of fun with this, and you'd be surprised by the imaginative and creative ideas that my pupils come up with.

Today the mystery object is a photograph (not a very good one) of a brass and enamelled wall plaque.

You will have to wait until later in the week to find out where this object is, and why it is important to me.