Larni writes:
I can't believe that nobody notice the missing 'd'.
Judging from some of the other letters (near where the 'd' should have been) it looks like it was possibly scratched off.
I agree that someone probably would have noticed a missing letter when it was being made.
But if it was removed later (e.g. by vandals) then I find it very believable that no-one had got around to getting it fixed.
"There is no great invention, from fire to flying, which has not been hailed as an insult to some god." J. B. S. Haldane