How about the sign that is used to stop people from letting their pets do their business? Ever seen those? Is there legal ramifications if you allow your dog to do its business where the sign asks you not to? How about a No Smoking sign? Ever notice some of these include wording about possible fines against those who don't adhere to it?
Maybe the sign for 'No Firearms' is there because previous signs for 'No Foul Play' or "Muggings Strictly Forbidden on these premises" weren't working?
On a more serious note, maybe the sign is posted as a suggestion by an insurance company who wishes to ward off any potential liability that may arise. Ever notice when you go to a sports arena, theres signs around there that say 'enter at your own risk. flying objects may cause injury'? What happens when someone does get hurt? They file a claim, don't they? The sign doesn't mean much of anything, it only occasionally dissuades someone who is not familiar with liability from possibly filing a claim. The insurance company still is going to follow through.
How about an amusement park? If you injure yourself on a ride, you are going to file a claim, right? But aren't there also signs at amusement parks that attempt to waiver the property owners or business owners liability?
If you slip and fall, hurt yourself on a wet floor that has a big yellow sign that warns of the danger, you are still able to file a claim, correct?
Signs are 'feel-good measures', when there is no legal ramifications for not obeying the suggestions of those signs.
"Every man alone is sincere; at the entrance of a second person hypocrisy begins." - Ralph Waldo Emerson
"People demand freedom of speech as a compensation for the freedom of thought which they seldom use." - Soren Kierkegaard