The "Ruptured Duck" was a cloth badge that enlisted people in WWII that they could wear on the right-hand pocket of their uniforms for 30 days after their discharge, a way to keep wearing their uniforms until they could afford to buy civilian clothes.
Many ruptured ducks have survived, and you can buy ruptured ducks on eBay for under $10, since ruptured ducks were handed out to millions of honorably discharged enlisted servicemen between 1943 and 1946:
Many discharged GI’s were too poor to buy civvies . . .
The name "ruptured duck" became a nice name for aircraft and anything related to enlisted veterans was a "ruptured duck",a sort of inside joke that onloy GI's knew about . . .
Here are some interesting renditions of a ruptured duck, ruptured duck logos: