FWIW, here is a link to a New York Times post re. the legality of photographing US government owned property. It may be worth saving the PDF on your laptop.
Interesting read.
That is how I understood it. However the deputy who detained me, photographed me next to the tag on my truck and then with my camera did not understand it that way.
James
Thank you, Andrew. Here's a direct link to the relevant doc.
I've three times been field interviewed by calm and informed professionals, each time hearing it was "okay" to take exterior pictures. It's good to know that, more than okay, it's a recognized right of citizenship.