Help... what is this thing?

I bought this little tag at a booth at my local antique mall. I thought the lion motif and numbers were very cool and would make a nice addition to one of my necklaces. Problem is I really don't know what it is or what it's purpose was. I am not sure how old it is either. I believe the GB would be for Great Britain, but other than that I don't have a clue. Anyone that can help me?