I seem to remember Walter (of the Wheelbarrow fame) mentioning that somewhere in the outskirts of Ewhurst, Surrey, there is a pole with a clearly readable 1940s date!
As for your high pole, it would be interesting to see images of the two markers . . . if Mrs Weaver could oblige, please. I'm not aware of any red plate but I do know of a label with a red capital D for dangerous and, thus, not to be climbed.