Verified answer

Hopefully some of these will give you some ideas...

"It needs to either encourage people to ration/recycle"

http://img.photobucket.com/albums/v336/unklebobosa...

[don't spend or waste fuel]

"buy war bonds"

http://ecx.images-amazon.com/images/I/51u%2Bb-Wm55...

[love the sinister implications if you don't buy, nice use of psychology]

"enlist in the armed forces"

http://history1900s.about.com/library/photos/blyww...

[offers a sense of belonging]

http://history1900s.about.com/library/photos/blyww...

[guilt and nationalsm being used]

"urge for greater war production"

http://history1900s.about.com/library/photos/blyww...

http://history1900s.about.com/library/photos/blyww...

[both playing on the fear card]

In most war posters, you try going for guilt, like you're not carrying your weight or you're letting everyone else do your fighting for you; or everyone else is concerving while you're being selfish and a glutton - perhaps costing people their lives; your man is off at the front so you should be in a factory making him the tools to do his job, his life is on the line if you don't.

The fear factor and patriotism were much used angles also, eg wife and kids at home so you gotta do your duty to keep them safe; or you gotta keep your mouth shut lest you spill and secret or give any info that can get your guy killed.

What country are you doing it for? The US, British Empire, Soviet Union, etc?

If it's US, make it look really patriotic and use red white and blue.

If it's British/Commonwealth make it proud and determined.

If it's Soviet make it patriotic and use red a lot.

If it's French make it determined and oppressed.

Caricaturing Hitler and the Nazis is always popular.

"connect the militia... See Europe." Or... "connect the army... See The Pacific." extra advantageous yet - "connect the Air Corps... See Europe from 20,000 ft." Or show a bomb falling and say "ENLIST! Slip Hitler the great One."