The counterculture of the era commonly appropriated gestures which were previously in support of war as protests against it. Examples of this include driving with headlights on (first in support of the war, then as protest, mentioned in Grossman's On Killing) and wearing parts of military uniforms and regalia.

The V-for-Victory gesture was used by Richard Nixon during his tenure to to signify victory in Vietnam, and started being used by protesters to symbolise peace after his resignation.

I'm curious how true the premise of the question is? From a British perspective I didn't think the meaning had changed, and the original meaning does seem to still persist in many places:

Libya a few years ago

The new Indian Prime Minister-designate

(I hope I can use these purely as examples of that, even though they are recent events)