ASC badge- where worn?

[badjez]

I have come into possession of a darkened GM ASC badge which is bigger than the usual collar badges, but smaller than the usual cap badges, and I don't know its purpose. I cannot see it in McHenry & Kellock's books. Can anyone illuminate me please?

I have not pictured the back as it has been messed with: a strip of metal, folded into blades has been superglued to the back! This obscures the reverse so I cannot tell what the original fittings were.

It measures 30x32mm.

Thanks in advance, Stephen.