I used to call this the 'trustee clearance'. In the agency I worked in, we had all kinds of restricted areas and highly confidential law enforcement information unique to those areas and only cleared personnel could be in there with the information. However, trustees on clean up details seemed to be able to go anywhere and everywhere. So we had a joke that you needed 'trustee clearance' which was above anything short of the Sheriff. It's a version of the brown truck clearance. UPS drivers seem to be able to just go anywhere without notice.