“...there’s a policy apparently against having any kind of weapons that are concealed in the building.”
Always follow policy. It’s the best policy.
I would follow the policy religiously, the sign says no weapons that are concealed in the building, I would assume that also means concealed upon your person inside the building.
Fine; I will wear my 45 Long Colt on a belt holster where GOD and everybody else CAN SEE IT!