The vision screen (Symbol)
The "vision screen" is a symbol of the opacity of the Overlords and their role on Earth; the fact that Stormgren cannot see Karellen while Karellen can see Stormgren is very clearly significant.
Deception (Motif)
There is a frequent motif of deception, lying, hiding, and subterfuge. Characters ranging from the Overlords to Jan to Stormgren to George conceal their motivations and actions from those they love or are in charge of. This deception is often done in order to protect or help others, but is complicated in that it may do more harm than good.
The red eye (Symbol)
The red eye is a symbol of the terrible might, power, and unknowable nature of the Overmind.
New Athens (Symbol)
New Athens is a symbol of the failure of utopias. It can never be fully isolated, and it can never fully meet the needs of its inhabitants. It is a microcosm of the larger world, which also suffers in its putative perfection.
The Overlords (Symbol)
The Overlords are symbols of both devils (e.g., Karellen-as-Antichrist) and guardian angels.