I've been wondering what the sign really means. I wondered if H28FT perhaps indicates the lamp post's height - but why? So, like any web-savvy person would do I did an image search for H28FT and found... ladders. How very strange, and yet possibly appropriate.
Do you know what these signs are/were used for? Do they perhaps indicate the height that the crane, used when changing light bulbs, should pick the workmen up to reach the light fixture?