Does the defense companies post a 30.06 and 30.07 type sign forbidding any kind of carry in the building?
I have never seen one but even if I did, it would just be CYA and not really necessary.
Virtually every DoD contractor employee handbook I have ever seen forbids bringing anything dangerous or hazardous into the workplace - especially firearms. Almost all of the person-to-person interaction is between DoD military, DoD government civilian, and DoD contractors and we are all covered by the same rules.
For some companies, it is a firing offense to even have a weapon in your car if it is parked on company property.
Of course, the high security and/or prime target facilities are fenced, controlled entrance operations with lots of armed guards. Like going through screening at an airport or at a courthouse entrance.