If you carry you are breaking the law and could be subject to but not limited to: termination by your employer, criminal prosecution, jail time, your CCW revoked, felony record.
Actually, it's a misdemenaor fine for trespassing just for carrying past the sign, if the owner wants to press it. Drawing the gun at the door to unload and store it is a whole different matter; that is probably unwise at best (I'm too polite to say "really dumb").
It seems to me the real issue is "Do you want to risk getting fired, which the company can do, whether you are arrested/charged or not?"