Seems like:

  - circle: city
  - triangle: factory
  - square: military base
  - big plane: bomber
  - little plane: fighter
  - things with rocket trails: ICBMs
  - floaty diamond things: satellites (which shoot down ICBMs)

The square in the middle of each team represents the current defcon. Assuming you start at defcon 5, when an enemy unit crosses the big blinking circle, drop to defcon 4. When a unit crosses the next blinking circle, drop to defcon 3. I haven't figured out yet how the escalation proceeds after that.