In the Chargemap pictures that probably date from 2020, there was no vertical sign. The spaces were painted with a blue square and a yellow EV symbol in the middle. I assume the vertical sign with blue disc indication was added at the same time the spots were painted yellow.
The signs I photographed back in 2022 were at least still current as of December 2023, because the same is visible on the &Charge pictures from that time. I can't find any more recent picture.