You work for the company and you are aware of their policies. The lack of a sign at the entrance of the parking lot does not render the aforementioned knowledge irrelevant. Current law in NC favors the right of the property owner over the right of the gun owner. Personally, I don't see a problem with that.
On the other hand, keep your mouth shut about your gun - meaning don't talk to your coworkers about shooting and carrying and that you carry all the time, etc etc etc and they should have no reason to suspect that you might have something in your vehicle. And if they did suspect - would you let them search your vehicle?