Since the setting is the Cold War era, it would make sense that there would be posters telling people that they should be uniting against a common enemy and leaving their Cold War squabbles behind.
Something like a handshake between a US and USSR soldier? (I'd suggest other nations, but US/USSR is how most people recall the cold war) You could always have a line of soldiers of different nations between the earth and a UFO.
Might have a go making one, but I'm not sure how good it would look.
[edit] attached a picture!
