Mentioning a previous discussion is intended to be a starting point, not to discourage further discussion. Especially here, where the answer addresses your question only briefly.

"Why was the practice of presenting men, who refused to enlist in the army, a white feather supported by early feminist organizations?" at https://www.reddit.com/r/AskHistorians/comments/3gisma/why_was_the_practice_of_presenting_men_who/ got only one answer, from /u/DuxBelisarius . He wrote about its use during World War I. He also wrote, "Some British women's organizations handed out feathers, an act that symbolizes 'cowardice' on the part of the receiver and which predated WWI.", but that's all it has on that. So I hope this induces the duke to expand rather than duck the question.

(Searching further, they also wrote about it in "Can you tell me how the white feather movement turned the tides of World War 1?" at https://www.reddit.com/r/AskHistorians/comments/4clspr/can_you_tell_me_how_the_white_feather_movement/ , with a link to a further posting. But those are purely about World War I and also include other topics.)