When Commander Prescott exits a building, he passes a sign that reads, "Flight Operations - Authorised Personnel Only". The film is set on an American Air Force base in New Mexico, and no sign in the United States would use the British spelling of "authorized", with an "s" instead of a "z". (The fact that the film was shot in England accounts for this error.)
In addition to the already-mentioned goof regarding one sign using the British spelling of "Authorised" instead of the American spelling (with a z instead of an s) that would be seen in New Mexico, Commander Prescott twice enters yet another building (the University of Albuquerque Aviation Medicine Dept.) with a sign reading "Scientific Station Authorised Personnel Only".
Though set in New Mexico, the film (except for some stock and establishment shots) was shot entirely in England, which is why scenes purportedly taking place in an arid state in the American southwest desert feature heavily forested areas with trees, hedges and shrubbery unknown in New Mexico, cold ground fog, and English-style houses and country roads.