Hi Juszach,
What age would your g-g-grandfather be in the photo? Do you know when it was taken? From what I can see it's pre-postcard and pre-gelatin prints, so could be from about 1900 at the latest - do you have the picture and can you show us the back of it?
Thinking this might help the railway experts to pin down a place/railway for you.
I did see some arms badges on the internet, for sale, that look like the one in the photo - they were for railway St John's Ambulance officers. It could be a shape common to other badges, though, I wouldn't know!
Prue