A Health "Clubbing"

The sign outside the Crosstown Lifetime Fitness Club reads: “Lifetime Fitness bans guns on these premises”.
I think, and then I thinks a second time,  when I sees a sign like this.  Has there been a problem here with club members carrying guns?  What has precipitated this sign?  Would a criminal be deterred by this sign? Is there any security in this Club?
 Recently 2 unarmed men broke into the Crosstown “Club” and severely beat and robbed a member who had no warning - or received any protection from the staff. The sign was his only protection. The attackers were caught later as the attackers continued their assaults at a nearby neighborhood residence.

This is not the Crosstown Club,  but one of the Lifetime Clubs.  One of my own stock photos.