Thanks for the feedback.
I got to spend a few more child free hours in the garage today and thought I'd take a few piccies of what I meant by the interchangeable sign system I had been working on:

Le Cateau in 1918



a few of the range of signs (I've made about 120 now )

a spot of Victorian science fiction...


The magnets hold them fairly well in place. They are just printed onto fridge magnet sheet. The fonts are period correct as far as I have researched (if anyone has more up to date knowledge or images then please do pass them on). They were created in Illustrator and the bullet marks etc are all added digitally. The VSF posters were quick photoshop exercises and frankly a bit of fun using aspects of existing WW1 posters!
I'll try to post more soon.