I have quite a few photos of old fire alarm bells. I was initially interested in the logos and typography, and the texture of the rusty old boxes. But just recently I noticed that a lot of them have pre-1966 telephone letter exchange codes on them.
Letter codes worked such that the first 3 letters of an area were used for that exchange, as in BIS 1234 = Bishopsgate 1234. You have probably heard a someone with clipped vowels in a 1940s film saying, "Mayfair 2743".
So I posted my most recent fire alarm pic to GWL and the interest was enough to set up a group to 'collect' them. I also realised I had others, embedded in pics of old shops signs etc.
There were 263 London codes, so I doubt we'll find existing examples of them all.
If you have seen any yourself, do let me know or add them to the group.
Below are some of the one I have found myself:
Middle row: Earlham Street, Wandsworth Road, Whitfield Street, Marylebone Lane
Bottom row: Curtain Road, Weston Park, Thornhill Road, Holloway Road