I visited RAND a few times in those days in connection with development of a small air to ground nuclear missile. I honestly don't remember the security system, probably because it was pretty typical of most places we went, but I do remember that everyone we saw had a large scale wall map of the LA area with "ground zero" at the LA City Hall, and circles around it showing the levels of damage from something like a 10 megaton blast. I still have the "blast damage calculator", a circular slide rule, that I was given as a RAND souvenir.
We did a lot of construction in secure military and defense instalations durring WW-2 and after and as far as I can remember outside of RAND and JPL if you had a note pad and a roll of plans under your arm no one would even ask who you were.
Even the Skunk Works at Burbank was less secure than RAND.