mod note: updated title to better reflect the subject
Once in a while I see an ICEd charging spot, and when I do, I leave one of these notes on the offending vehicle:
Thumbnail view of the form:
I fill out the blank with their license plate number and then publish their offense and plate at Zapatag.com - Report Bad Drivers, License Plate Search and Tracking. Fold the note in thirds along the dashed lines, with the wording visible on the outside, and attach to the offending vehicle's windshield. I carry about 20 of these in my car and use them as appropriate.