Does anyone know why all of the Temporary Signs on London Overground
stations have been replaced with permanent signs which appear to be
identical to the temporary ones in every way, except that they don't
have "Temporary Sign' written on them?

(This reminds me of the bit in Grimble where the fridge contains nothing
but a biscuit bearing the message in green ink "Do not eat this biscuit,
as green ink is poisonous".)