I started seeing similar signs in Nevada earlier this year.
Nevada Revised Statute.
NRS?484B.468??Parking space designated for charging electric or hybrid electric vehicles: Signs; prohibited acts; penalties.
1.??A person shall not park a vehicle in a space designated for charging electric or hybrid electric vehicles by a sign or
markings that meet the requirements of subsection 2, whether on public or privately owned property, if the vehicle is not
connected to the charging station for the purpose of charging.