Mind you, when it's phrased like
that, they're going for LEED credits, and there's actually a list of vehicles eligible for those spaces:
greenercars.org | news & documents
So technically, if your vehicle is not on that list, you are not allowed to use that space. And, many vehicles that are quite fuel efficient don't have the emissions performance to make the list. Now, nobody would even think twice if you, say, parked an old TDI there (which due to emissions performance doesn't even come close to meeting the list), but still.