I've found this solid metal stamp saying 'AIR RAID'. What would this have been used for? | AskHistorians Archive Observer

I've found this solid metal stamp saying 'AIR RAID'. What would this have been used for?

by wigchest

https://imgur.com/a/kAESSaS

Would really appreciate discovering what this could have been used for.

wigchest

I should mention it was found in a WW2 British civilian gas mask box.