Take the test drive, waste their time in negotiations then tell them you saw the sign and will go buy a similar vehicle at another dealership. It's his right to post but it is your right to purchase or not. It only hurts them if they KNOW they lost a sale.
Last time I looked at the Kentucky laws (when I was there in march), any business could post a gun buster sign, but only for certain businesses is the sign enforceable. I'm sure they can always try to get you for trespassing of they ask you to leave and you don't.
Check the laws and see if they changed, but I suspect that you can conceal carry in there with no legal repercussions.
My original post was to alert others that a local business was foolishly advertising itself as a soft target by openly prohibiting firearms on its premises (I suppose I misunderstood the intended purpose of this thread - "businesses against firearms and the 2nd amendment"). I know the laws here and what a business can and cannot do - I was letting people know they may want to look for a Ford or service elsewhere - but thanks to the others for their input. The dealership KNOWS it lost a sale because of its policy and that potential customers would be steered to dealerships not run by idiots.