A simpler and cheaper solution would be to fix those availability signs. Surely this is not a problem that a few cameras and some smart software couldn't solve.
When I got back I walked past the kiosk that said "type in your license plate and locate your car" for those who forgot where they parked, like I did. Typed it in - no car found. (this was a recent trip, out on 07/23 and back on 07/25)