(X-POST from /r/nursing) My great aunt Alice served as a nurse in Salonika, Greece, during WW1, so I'm not sure if this should be here or in /r/military, but if anyone can help me find the significance of this badge she left, it would mean a lot to my family and I, as we are currently going through her things and cataloging everything.
That is a WWI era Yugoslavian/Serbian officers cockade cap badge. I believe they are pretty rare. Usually those pins had blue in the center and red on the outside. It is from the Yugoslavian "Kingdom era" 1918-1939 Hope that answered some questions.
Edit to add example: http://www.jkmilitaria.com/Serbia.html
Just a little way down the page youll see the same badge and description.