The VA Hospital in Muskogee OK and the Out Patient Clinic in Tulsa are posted, but the 2 Mental health clinics are not posted. Both of these are only partially leased by the Government. To make matters worse the building where the MH Clinic in located in Tulsa is not posted. You can carry into the building, and the only sign you see is a Gunbuster sign on the door going into the clinic.
The VA law is under 38 USC, 18 USC applies to Government building in general. The Social Security Office and the Post Offices here in Oklahoma aren't posted in the parking lots, just at the front door.
38 USC gives the VA the authority to operate, by the 38 CFR are the Regulations that thew VA write, and these cant exceed the authority given the them by the USC.