Hi Alli
I've been sleeping on (oooh, errr missus....!) your Buffs badge and I think that what we THINK is a hallmark on the back of the the wee enamel centre is actually from the striking of the badge.
I think that I read somewhere they would often use something like a piece of leather or wet(!) cardboard as this meant that the metal didn't need to be quite as think and the raised detail came up sharper. This possible "hallmark" is from the backing material.
Cheers
Mr N.G.