All that typically matters to an insurance company is that the question is asked "Do you have firearms on premises?" And that question is not directly pointed to actions of the insureds customers, its about the insured and their employees.
Agreed. And they base their rates on the answers to such questions. An insurance company may not require
a business to have sprinklers... but if it makes a major difference to the premium, it can come to the same thing. If a "no guns" sign lowered the rate for liability insurance, a business, or other organization, might need to post one, especially if it were struggling in the current economy.
Mileage varies. The new Wisconsin concealed carry law immunizes businesses that don't prohibit guns from civil liability claims, but not those that do. That's not the case in Minnesota.