Anything but US in Vietnam (done to death). How about Royal Lao Air Force. They used the Discworld Roundels.

I'll print you a set if you want.
Technically speaking, aren't those
Coneworld roundels rather than Discworld ones?
Coneworld is similar to Discworld except that:
a. it's got more surface area
b. the inhabitants are fitter
c. the inhabitants are more pished off
d. anyone who proposed a karting competition is put on suicide watch immediately