I generally try to stay out of MD so I’m not sure if shopping malls tend to be specifically posted or not, but the point is moot. The discretionary concealed handgun license in MD is off limits to anyone not politically connected, and they have no reciprocity with any other state. So posted or not, the mall is a free-fire zone for the criminal class.
I pretty much try to stay out of MD, which isn’t all that hard because I live in Texas.
However, we did drive to Washington DC not long ago, and that made it harder.
Let’s just say I got around the law pretty well.