Oh how I feel your pain. Many years ago, while trying to negotiate a very tight parking area, I managed to crunch my fender with the warning post. Always figured the parking lot people should have paid for the repairs because their post certainly didn't do its assigned job!!
And just last week I barely (and I mean by the barest of barely) managed to NOT scrape the top of my car. Who sticks a sign 6 feet into a parking spot without putting a barrier below the sign??