Spotters followed specific protocols in monitoring the skies for aircraft.
This file appears in: Eyes to the Skies!: Civil Defense Volunteers Ensured Safety and Posterity

Barb Mortenson of Gorham, New Hampshire demonstrates binoculars’ restricted use to identify planes. Actual ground observing or “spotting” was done with the naked eyes. Spotters followed specific protocols in cooperation with the United States Air Force. Image courtesy United States Library of Congress.
This file appears in: Eyes to the Skies!: Civil Defense Volunteers Ensured Safety and Posterity
Eyes to the Skies!: Civil Defense Volunteers Ensured Safety and Posterity
Ground Observer Corps volunteers support Air Force command in protection from Soviet air attacks