Weird Signs

Below pictures are of my husband and the baby. These were taken outside the USCIS parking lot when we went there 4 weeks ago. My husband wanted his pictures taken by the weird signs probably for remembrance? As you see it, all parking spots with signs in it are vacant. Nobody parked their car in those spots, I wonder why? And why would a government agency put such signs?

.....the sign says RESERVED PARKING
LOW-EMITTING/FUEL EFFICIENT VEHICLES ONLY