I was looking recently at some of my older leaves, which are marked "BCM/Filofax".
I realised that I had no idea why they said that, or what BCM actually stood for. Searching the Philofaxy archives didn't help either - several mentions of the inscription, but no explanation.
I decided to hunt a bit wider. In 1925 a chap called William Morris started a company called British Monomarks, with the aim of providing a Post Office box and mail forwarding service using the shortest possible addresses. Each subscriber would have a unique code, and their address would prefix this with BM (or BCM), follow it by "London" and that would suffice. The company had a special arrangement with the Post Office.
So it seems BCM actually stands for "British Commercial Monomarks", and "BCM/Filofax" serves as the correspondence address. It's very similar to printing a URL nowadays.
In fact British Monomarks are still going, and provide virtual office services.
I don't know when Filofax started or stopped this. I found some evidence online that they were using it in the 1960s, and my guess would be that this continued until around 1980.
If anyone can add more details I'd be interested to hear!
Thank you once again Max for another guest post.