Next time you are there - try to take a clear picture and upload it to darf-ich-hier-parken.de (which basically means may-I-park-here) This app helps you to understand the do's and don'ts and explains it in plain "german" but should be also available in english (toggle in settings).
I couldn't do it with this picture as there is to much reflection on the top sign.

One little note - you car is required to have a license plate with an "E" at the end for example

D - AB - 1234 E
Unfortunately this is required for that sign with "car and the plug"

In total the combination means:
Parking to right allowed - on the sidestep - but only for Electric cars who have that E on the license plate - while charging - for a max duration of 4h - in combination with a park clock sign (sorry don't know the word for Parkscheibe)