If there are no signs, That would make it an employment policy and since the Supreme court ruled that Police do not have a responsibility to protect any individual, I don't see how the company can do more than have you escorted off the property.
My company has a similar policy, I have been complying with it because in the machine shop where I work there are enough cover and expediant weapons that I'm not concerned, However, I usually walk to work and after a serious look at potential threats, I think I may be in more danger from dogs and Bears ( saw one right outside the window last fall) unfortunatly none of my current pistols are small enough for DEEP concealment. My current solution is to carry a boot clip equipped folding knife, should give me some chance with dogs and if I run into a bear I can throw poop at it, I know where I'll be able to find THAT.