Having lived in many of the states comprising this great country of ours, I know for a fact that if a place I intend to visit has a posted "No Firearms" rule, then I make every effort to abide by that rule.
That's whether it's a courthouse, municipal building, tavern, store, parking lot, or gas station.
I've actually caught myself mid-stride to turn around and lock up my CCW piece in my vehicle's safe place.
We sure's hell may not like it, but it's the law of the land.
Some choose to ignore policy, for various reasons.
Again, you choose to defy your employer's no-gun policy, and after the shootout you've so diligently prepared for, you're going to get fired, at best.
At worst, your CCW may be scrutinized, or your employer could sue you, etc.
It's your version of risk management. Mine's a little different. Just because I have a CCW permit does not make me large and in charge. You pick your fights carefully, and if you feel you must violate your employer's property rights with your CCW, I'd suggest not advertising so on a very public internet forum.