That is a very technical argument. I think it has a chance of succeeding; but I sure wouldn't bet my own money that way.
I think it would actually be harder to sell the idea that it should be seen as a general notice.
First of all, it's extremely specific. Both the carefully specified sign and the wording of the law apply exclusively to license holders. If one can twist the law to apply it to "non-license holders" even when it clearly says it applies to "license holders" then it would be equally reasonable to claim that it prevents anyone from entering the premises with any kind of weapon at all even though it only applies to handguns. If the courts can essentially change the meanings of the words in the laws then we'd only need one law and we'd expand and extend or invert the meaning of whichever words we needed to in order to make our one law apply to the specific case at hand.
Second, at the time it was passed, car carry was illegal without a license, so it makes no sense to claim that it was intended to give general notice to those carrying without a license. Saying it's meant to apply to those carrying under the auspices of the car carry law would be like saying that a speeding law passed in the late 1800s preventing anyone from travelling over 40 mph in a horseless carriage was meant to apply to airplanes as well even though airplanes hadn't been invented yet when the law was passed.