"Excuse me, we're looking for Sierra 7." "Yeah, it's down this road for a mile, then left on 127."
And the Soviets wouldn't have been fooled either. So they look like military installations.
http://www.nytimes.com/2015/01/15/us/roswell-new-mexico-miss...
More morbidly, in a first strike scenario you want the enemy to waste nukes on actual farmhouses it couldn't tell for certain were launch facilities or not. Then even if no facilities are missed (something you would be hoping for), that's still fewer nukes to be dropped on cities and conventional military installations.
They just copied some footage helpfully provided by the air force. (7:50) There must have been a "director's cut" of the same because we see it in "The Day After" where they're turning the keys.