I don't buy that the insurance companies dictate such signage. I have been in business for myself for 30 years and buying commercial insurance for that long, and I have never had an insurance company make any inquiry about firearms on the premises or firearm policies, or any other signage or safety issues besides OSHA compliance. Insurance companies deal with big blocks of customers, and they don't customize the coverage or restrictions on each business individually.
There is a real dichotomy when these complaints come up, in that the same forums that host threads denouncing such restrictions also host threads in which writers say they have witnessed dangerous mishandling of firearms. I don't agree that a well-trained and well-disciplined CCL holder should have to disarm, I am also aware that not everyone who goes to a gun store, range, or gun show is well-trained, well-disciplined, or licensed. Even though I might not agree, I can respect the fact that the proprietors are making a good-conscious effort at keeping themselves and their customers (including me) safe.