I have managed to contact Richard Humphry, who was the founder of the Alan Turing Memorial fund, with regards to the code on the banch and whether he could shine any light on what it was intended to encode. Unfortunately for those wanting a definitive answer, this was his response:
I wish I could assist you as to the translation of the Enigma Code inscription on the bench behind the figure but this is a secret so closely guarded by the sculptor/designer, Glyn Hughes that he wouldn’t tell even me what it meant. He was somehow able to access the daily rotor positions of the Enigma machine but he wouldn’t divulge which day he had chosen!
It would appear that Glyn (or someone he was working with at the time) was the originator of the code. Given his response to my earlier query, he is unable to or unwilling to divulge both the secret of the encoding and its intended message.
If Glyn does actually know the secret and is unwilling to share it as it would compromise the artistic integrity or message of his piece, then so be it. There is a sort of poetry in an intrinsically unsolvable code added to a memorial, a memorial that reminds us of the loss of Alan Turing – suggesting that this might not remain unsolvable if his life hadn’t been cut so short.
It is up to us, therefore, to assign a meaning to the message and out of a number of suggestions made by people on twitter, I prefer the following statement by @dwauctioneer(also chosen by Simon Singh as his favourite):
“Communication will unite us“
A fitting message I think.