In the malls I’ve gone to (including my prime one, shot up a few years ago in another incident), I’ve never seen any signs posted in all my life. Nor for all the other rules they have. They can be found on websites.
I have seen a number of Malls with No Gun signs.
One of the most prominent is Mall of the Americas, near Minneapolis.
The Crossroads Mall, recent scene of the mass stabbing in St. Croix, has them.
http://gunwatch.blogspot.com/2016/09/jihad-mass-stabbing-st-cloud-mall-was.html