At the root of this issue is that the NRS indicates only concealed carry is prohibited "A permittee shall not carry a concealed firearm while the permittee is on the premises of..."
but the NRS says to display a sign that states no firearms are allowed.
"A public building that has a metal detector at each public entrance or a sign posted at each public entrance indicating that no firearms are allowed in the building, unless the permittee is not prohibited from carrying a concealed firearm while he or she is on the premises of the public building pursuant to subsection 4."
The DMV at Fallon says concealed waepons. I'll have to get a picture of it. I guess they didn't obey the statute to the letter of the law.
I'm also guessing the other DMV's and police/sheriffs offices are just making the signs in accordance with the NRS, which says "no firearms". But, then they want to enforce the law, the way the sign reads, even though we know, that's not the way the law is written.