If it's private property, I respect the owners wishes. If I think those are absurd, I go elsewhere. Kinda like places with "No concealable weapons" signs.
I did see 'hybrid parking' signs at town hall once. I parked there and came out to a cop hanging around my truck. He questioned me about it and I told him that it ran on the souls of crushed prius', gasoline and leg power and proceeded to push my truck out of the space as a demonstration. He laughed his ass off and we bullshitted about my truck fro 15 minutes before I left.