It is not about getting criminals to follow laws, criminals do though often follow a rule of conduct. If you can eraduicate the need for a gun from their mentality them you are already one up on them. When a culture actively encourages firearm possessions it is also doing so inadvertantly on the criminal fraternity.
It is not a black and white issue of laws or no laws. You have to understand that regardless of the laws overhere, when a person walks into a public place with a firearm they are deemed as nothing but scum, there is no honour or privelage for them to have they are nothing but some of the lowest form of human life.This attitude is implemented throughout society here, some of the innercity gangs are admittedly adopting the US attitude where having a gun makes you king, but the general consencus of things including that of the criminal element is that a gun is a dirty tool that will only attract you trouble, there is no honour.
Try and understand this process with this way of thinking; a terrorist endangers society. How do you feel about terrorists! ...Now change the terrorist concept to one of guns in public and you might start to understand the difference in attitudes.
The US does not need to change its gun laws, it does not need to change its gun control, it needs to change its gun culture. You cant fight this culture, because as hard as you fight it, it will always fight back. So how do you go about telling the criminals that they dont need guns? How do you tell the murderers that pulling that trigger was not the easy option? How do you tell the kid walking into a school/mall whilst intent to do harm that his actions will not be the making of him, that the actions are immoral and have no honour? ......tbh when I see the gun advocation or the continued sensationalism around guns, all that is happening is you encourage these problems, this brazen attitude that feeds you also feeds them. You have "Firearm Advocate!" in your user title, I just hope you realise that by advocating firearms in one walk of life you advocate them in all walks of life and that includes when the devil has his finger at the trigger.
Returning to the OP, by having a sign on a wall saying "Gun free zone" you are basically saying that this area is designated safe from guns do not go and spoil the party because if you do then you really are scum.